Esperanto (/ˌɛspəˈrɑːntoʊ, -ˈræn-/)^[8][9] is the most widely spoken constructed international auxiliary language. It was created in the late 19th century by L. L. Zamenhof. In 1887 he published a book detailing the language, Unua Libro ("First Book"), under the pseudonym Dr. Esperanto. Esperanto translates to English as "one who hopes".^[10]

Zamenhof's goal was to create an easy and flexible language that would serve as a universal second language to foster peace and international understanding, and to build a community of speakers, as he believed that one could not have a language without a community of speakers.^[11]

His original title for the language was simply the international language (lingvo internacia), but early speakers grew fond of the name Esperanto and began to use it as the name for the language in 1889; the name quickly gained prominence and has been used as an official name ever since.^[12]

In 1905, Zamenhof published Fundamento de Esperanto as a definitive guide to the language. Later that year, he organized the first World Esperanto Congress, an ongoing annual conference, in Boulogne-sur-Mer, France. The first congress ratified the Declaration of Boulogne, which established several foundational premises for the Esperanto movement. One of its pronouncements is that Fundamento de Esperanto is the only obligatory authority over the language. Another is that the Esperanto movement is exclusively a linguistic movement and that no further meaning can ever be ascribed to it. Zamenhof also proposed to the first congress that an independent body of linguistic scholars should steward the future evolution of Esperanto, foreshadowing the founding of the Akademio de Esperanto (in part modeled after the Académie française) which was established soon thereafter. Since 1905, congresses have been held in various countries every year, with the exceptions of years during the World Wars. In 1908, a group of young Esperanto speakers led by Hector Hodler established the Universal Esperanto Association, in order to provide a central organization for the global Esperanto community.

Esperanto grew throughout the 20th century, both as a language and as a linguistic community. Despite speakers facing persecution in regimes such as Nazi Germany and the Soviet Union under Stalin,^[13] Esperanto speakers continued to establish organizations and publish periodicals tailored to specific regions and interests. In 1954, the United Nations granted official support to Esperanto as an international auxiliary language in the Montevideo Resolution.^[14] Several writers have contributed to the growing body of Esperanto literature, including William Auld, who received the first nomination for the Nobel Prize in Literature for a literary work in Esperanto in 1999, followed by two more in 2004 and 2006. Esperanto-language writers are also officially represented in PEN International, the worldwide writers association, through Esperanto PEN Centro.^[15]

Esperanto has continued to develop in the 21st century. The advent of the Internet has had a significant impact on the language, as learning it has become increasingly accessible on platforms such as Duolingo and as speakers have increasingly networked on platforms such as Amikumu.^[16] With approximately two million speakers, a small portion of whom are native speakers,^[5] it is the most widely spoken constructed language in the world.^[17] Although no country has adopted Esperanto officially, Esperantujo is the collective name given to places where it is spoken, and the language is widely employed in world travel, correspondence, cultural exchange, conventions, literature, language instruction, television and radio broadcasting.

While its advocates continue to hope for the day that Esperanto becomes officially recognized as the international auxiliary language, an increasing number have stopped focusing on this goal and instead view the Esperanto community as a "stateless diasporic linguistic minority" based on freedom of association, with a culture worthy of preservation based on its own merit.^[18] Some have also chosen to learn Esperanto due to its purported help in third language acquisition.

Zamenhof had three goals, as he wrote in Unua Libro:

According to the database Ethnologue (published by the Summer Institute of Linguistics), up to two million people worldwide, to varying degrees, speak Esperanto,^[21] including about 1,000 to 2,000 native speakers who learned Esperanto from birth.^[22] The Universal Esperanto Association has more than 5500 members in 120^[23] countries. Its usage is highest in Europe, East Asia, and South America.^[24]

Lernu! is one of the most popular on-line learning platforms for Esperanto. Already in 2013, the "lernu.net" site reported 150,000 registered users and had between 150,000 and 200,000 visitors each month.^[25] Lernu currently has nearly 291,000 registered users, who are able to view the site's interface in their choice of 23 languages – Catalan, Chinese (both simplified and traditional characters) Danish, English, Esperanto, Finnish, French, Georgian, German, Hebrew, Hungarian, Italian, Kirundi, Kiswahili, Norwegian (Bokmål), Persian, Portuguese, Romanian, Russian, Serbian, Slovak, Swedish and Ukrainian; a further six languages — Bulgarian, Croatian, Czech, Dutch, Indonesian and Spanish – have at least 60 percent of the interface localized; nine additional languages – Greek, Japanese, Korean, Lithuanian, Polish, Slovenian, Thai, Turkish and Vietnamese – are in varying stages of completing the interface translation. About 50,000 lernu.net users possess at least a basic understanding of Esperanto.

With about 269,000 articles, Esperanto Wikipedia (Vikipedio) is the 32nd-largest Wikipedia, as measured by the number of articles,^[26] and is the largest Wikipedia in a constructed language.^[27] About 151,000 users consult the Vikipedio regularly.

On February 22, 2012, Google Translate added Esperanto as its 64th language.^[28] On July 25, 2016, Yandex Translate added Esperanto as a language.^[29]

On May 28, 2015, the language learning platform Duolingo launched a free Esperanto course for English speakers.^[30] On March 25, 2016, when the first Duolingo Esperanto course completed its beta-testing phase, that course had 350,000 people registered to learn Esperanto through the medium of English. As of 27 May 2017, over one million users had begun learning Esperanto on Duolingo;^[31] by July 2018 the number of learners had risen to 1.36 million. On July 20, 2018, Duolingo changed from recording users cumulatively; it now reports only the number of "active learners", i.e., those who are currently studying, but not those who have completed the course.^[32] On October 26, 2016, a second Duolingo Esperanto course, for which the language of instruction is Spanish, appeared on the same platform^[33] and currently has a further 306,000 students. A third Esperanto course, taught in Brazilian Portuguese, began its beta-testing phase on May 14, 2018, and 179,000 people are currently using this course to learn the international language. Esperanto is now one of 27 courses that Duolingo teaches through English, one of nine courses taught through Spanish and one of six courses taught through Portuguese.

Esperanto was created in the late 1870s and early 1880s by L. L. Zamenhof, a Polish-Jewish ophthalmologist from Białystok, then part of the Russian Empire but now part of Poland. According to Zamenhof, he created the language to reduce the "time and labour we spend in learning foreign tongues" and to foster harmony between people from different countries: "Were there but an international language, all translations would be made into it alone ... and all nations would be united in a common brotherhood."^[20] His feelings and the situation in Białystok may be gleaned from an extract from his letter to Nikolai Borovko:^[34]

About his goals Zamenhof wrote that he wants mankind to "learn and use", "en masse", "the proposed language as a living one".^[20] The goal for Esperanto to become a general world language was not the only goal of Zamenhof; he also wanted to "enable the learner to make direct use of his knowledge with persons of any nationality, whether the language be universally accepted or not; in other words, the language is to be directly a means of international communication."^[20]

After some ten years of development, which Zamenhof spent translating literature into Esperanto as well as writing original prose and verse, the first book of Esperanto grammar was published in Warsaw on July 26, 1887. The number of speakers grew rapidly over the next few decades, at first primarily in the Russian Empire and Central Europe, then in other parts of Europe, the Americas, China, and Japan. In the early years, speakers of Esperanto kept in contact primarily through correspondence and periodicals, but in 1905 the first World Congress of Esperanto speakers was held in Boulogne-sur-Mer, France. Since then world congresses have been held in different countries every year, except during the two World Wars. Since the Second World War, they have been attended by an average of more than 2,000 people and up to 6,000 people.

Zamenhof's name for the language was simply Internacia Lingvo ("International Language").^[35]

The autonomous territory of Neutral Moresnet, between what is today Belgium and Germany, had a sizable proportion of Esperanto-speakers among its small and multi-ethnic population. There was a proposal to make Esperanto its official language.

However, neither Belgium nor Prussia (now within Germany) had ever surrendered its original claim to it. Around 1900, Germany in particular was taking a more aggressive stance towards the territory and was accused of sabotage and of obstructing the administrative process in order to force the issue. It was the First World War, however, that was the catalyst that brought about the end of neutrality. On August 4, 1914, Germany invaded Belgium, leaving Moresnet at first "an oasis in a desert of destruction".^[36] In 1915, the territory was annexed by the Kingdom of Prussia, without international recognition.

After the Great War, a great opportunity seemed to arise for Esperanto when the Iranian delegation to the League of Nations proposed that it be adopted for use in international relations, following a report by Nitobe Inazō, an official delegate of the League of Nations during the 13th World Congress of Esperanto in Prague.^[37] Ten delegates accepted the proposal with only one voice against, the French delegate, Gabriel Hanotaux. Hanotaux opposed all recognition of Esperanto at the League, from the first resolution on December 18, 1920 and subsequently through all efforts during the next three years.^[38] Hanotaux did not like how the French language was losing its position as the international language and saw Esperanto as a threat, effectively wielding his veto power to block the decision. However, two years later, the League recommended that its member states include Esperanto in their educational curricula. The French government retaliated by banning all instruction in Esperanto in France's schools and universities .^{[39] [40]} The French Ministry Of Instruction said that "French and English would perish and the literary standard of the world would be debased".^[41] Nonetheless, many people see the 1920s as the heyday of the Esperanto movement. Anarchism as a political movement was very supportive during this time of anationalism as well as of the Esperanto language.^[42]

Esperanto attracted the suspicion of many states. The situation was especially pronounced in Nazi Germany, Francoist Spain up until the 1950s, and in the Soviet Union from 1937 to 1956.

In Nazi Germany, there was a motivation to forbid Esperanto because Zamenhof was Jewish, and due to the internationalist nature of Esperanto, which was perceived as "Bolshevist". In his work, Mein Kampf, Adolf Hitler specifically mentioned Esperanto as an example of a language that could be used by an international Jewish conspiracy once they achieved world domination.^[13] Esperantists were killed during the Holocaust, with Zamenhof's family in particular singled out for being killed.^[43] The efforts of a minority of Esperantists to expel Jewish colleagues and align themselves with the Reich were futile and Esperanto was legally forbidden in 1935. Esperantists in German concentration camps taught the language to fellow prisoners, telling guards they were teaching Italian, the language of one of Germany's Axis allies.^[44]

In Imperial Japan, the left-wing of the Japanese Esperanto movement was forbidden, but its leaders were careful enough not to give the impression to the government that the Esperantists were socialist revolutionaries, which proved a successful strategy.^[45]

After the October Revolution of 1917, Esperanto was given a measure of government support by the new workers' states in the former Russian Empire and later by the Soviet Union government, with the Soviet Esperanto Association being established as an officially recognized organization.^[46] In his biography on Joseph Stalin, Leon Trotsky mentions that Stalin had studied Esperanto.^[47] However, in 1937, at the height of the Great Purge, Stalin completely reversed the Soviet government's policies on Esperanto; many Esperanto speakers were executed, exiled or held in captivity in the Gulag labour camps. Quite often the accusation was: "You are an active member of an international spy organisation which hides itself under the name of 'Association of Soviet Esperantists' on the territory of the Soviet Union." Until the end of the Stalin era, it was dangerous to use Esperanto in the Soviet Union, despite the fact that it was never officially forbidden to speak Esperanto.^[48]

Fascist Italy allowed the use of Esperanto, finding its phonology similar to that of Italian and publishing some tourist material in the language.

During and after the Spanish Civil War, Francoist Spain suppressed anarchists, socialists and Catalan nationalists for many years, among whom the use of Esperanto was extensive,^[49] but in the 1950s the Esperanto movement was again tolerated.^[50]

Esperanto has not been a secondary official language of any recognized country, but it entered the education system of several countries such as Hungary^[51] and China.^[52]

There were plans at the beginning of the 20th century to establish Neutral Moresnet as the world's first Esperanto state. In addition, the self-proclaimed artificial island micronation of Rose Island used Esperanto as its official language in 1968, and another micronation, the extant Republic of Molossia, uses Esperanto as an official language alongside English.^[53]

The Chinese government has used Esperanto since 2001 for daily news on china.org.cn. China also uses Esperanto in China Radio International and for the internet magazine El Popola Ĉinio.^[54]

The Vatican Radio has an Esperanto version of its website.^[55]

The US Army has published military phrase books in Esperanto,^[56] to be used from the 1950s until the 1970s in war games by mock enemy forces.

Esperanto is the working language of several non-profit international organizations such as the Sennacieca Asocio Tutmonda, a left-wing cultural association which had 724 members in over 85 countries in 2006.^[57] There is also Education@Internet, which has developed from an Esperanto organization; most others are specifically Esperanto organizations. The largest of these, the Universal Esperanto Association, has an official consultative relationship with the United Nations and UNESCO, which recognized Esperanto as a medium for international understanding in 1954.^[58][59] The World Esperanto Association collaborated in 2017 with UNESCO to deliver an Esperanto translation^[60] of its magazine UNESCO Courier (Unesko Kuriero en Esperanto).

Esperanto is also the first language of teaching and administration of the International Academy of Sciences San Marino.^[61]

In the summer of 1924, the American Radio Relay League adopted Esperanto as its official international auxiliary language, and hoped that the language would be used by radio amateurs in international communications, but its actual use for radio communications was negligible.

All the personal documents sold by the World Service Authority, including the World Passport, are written in Esperanto, together with English, French, Spanish, Russian, Arabic, and Chinese.^[62]

Zamenhof's goal to "enable the learner to make direct use of his knowledge with persons of any nationality, whether the language be universally accepted or not",^[20] as he wrote in 1887, has been achieved, as the language is currently spoken by people living in more than 100 countries.

On the other hand, one common criticism made is that Esperanto has failed to live up to the hopes of its creator, who dreamed of it becoming a universal second language.^[63][64] In this regard it has to be noted that Zamenhof was well aware that it might take much time, maybe even many centuries, to get this hope into reality. In his speech at the World Esperanto Congress in Cambridge in 1907 he said, "we hope that earlier or later, maybe after many centuries, on a neutral language foundation, understanding one each other, the nations will build ... a big family circle."^[65]

The Esperanto alphabet is based on the Latin script, using a one-sound-one-letter principle, except for [d͡z]. It includes six letters with diacritics: ĉ, ĝ, ĥ, ĵ, ŝ (with circumflex), and ŭ (with breve). The alphabet does not include the letters q, w, x, or y, which are only used when writing unassimilated foreign terms or proper names.

The 28-letter alphabet is:

All unaccented letters are pronounced approximately as in the IPA, with the exception of c. Esperanto j and c are used in a way familiar to speakers of many European languages, but unfamiliar to most English speakers: j has a y sound [j~i̯], as in yellow and boy, and c has a ts sound [t͡s], as in hits or the zz in pizza.^[66] The accented letters are a bit like h-digraphs in English: Ĉ is pronounced like English ch, and ŝ like sh. Ĝ is the g in gem, ĵ a zh sound, as in fusion or French Jacques, and the rare ĥ is like the German Bach, Scottish Gaelic, Scots and Scottish Standard English loch, or how Scouse people sometimes pronounce the 'k' in book and 'ck' in chicken.

Even with the widespread adoption of Unicode, the letters with diacritics (found in the "Latin-Extended A" section of the Unicode Standard) can cause problems with printing and computing, because they are not found on most physical keyboards and are left out of certain fonts.

There are two principal workarounds to this problem, which substitute digraphs for the accented letters. Zamenhof, the inventor of Esperanto, created an "h-convention", which replaces ĉ, ĝ, ĥ, ĵ, ŝ, and ŭ with ch, gh, hh, jh, sh, and u, respectively.^[67] If used in a database, a program in principle could not determine whether to render, for example, ch as c followed by h or as ĉ, and would fail to render, for example, the word senchava properly. A more recent "x-convention" has gained ground since the advent of computing. This system replaces each diacritic with an x (not part of the Esperanto alphabet) after the letter, producing the six digraphs cx, gx, hx, jx, sx, and ux.

There are computer keyboard layouts that support the Esperanto alphabet, and some systems use software that automatically replaces x- or h-convention digraphs with the corresponding diacritic letters (for example, Amiketo^[68] for Microsoft Windows, Mac OS X, and Linux, Esperanta Klavaro for Windows Phone,^[69] and Gboard and AnySoftKeyboard for Android).

Criticisms are made of the letters with circumflex diacritics, which some find odd or cumbersome, along with their being invented specifically for Esperanto rather than borrowed from existing languages; as well as being arguably unnecessary, as for example with the use of ĥ instead of x and ŭ instead of w.^[70]

The phonology, grammar, vocabulary, and semantics are based on the Indo-European languages spoken in Europe. The sound inventory is essentially Slavic, as is much of the semantics, whereas the vocabulary derives primarily from the Romance languages, with a lesser contribution from Germanic languages and minor contributions from Slavic languages and Greek. Pragmatics and other aspects of the language not specified by Zamenhof's original documents were influenced by the native languages of early authors, primarily Russian, Polish, German, and French. Paul Wexler proposes that Esperanto is relexified Yiddish, which he claims is in turn a relexified Slavic language,^[71] though this model is not accepted by mainstream academics.^[72]

Esperanto has been described as "a language lexically predominantly Romanic, morphologically intensively agglutinative, and to a certain degree isolating in character".^[73] Typologically, Esperanto has prepositions and a pragmatic word order that by default is subject–verb–object. Adjectives can be freely placed before or after the nouns they modify, though placing them before the noun is more common. New words are formed through extensive prefixing and suffixing.

Esperanto words are mostly derived by stringing together roots, grammatical endings, and at times prefixes and suffixes. This process is regular, so that people can create new words as they speak and be understood. Compound words are formed with a modifier-first, head-final order, as in English (compare "birdsong" and "songbird," and likewise, birdokanto and kantobirdo). Speakers may optionally insert an o between the words in a compound noun if placing them together directly without the o would make the resulting word hard to say or understand.

The different parts of speech are marked by their own suffixes: all common nouns end in -o, all adjectives in -a, all derived adverbs in -e, and all verbs except the jussive (or imperative) end in -s, specifically in one of six tense and mood suffixes, such as the present tense -as; the jussive mood, which is tenseless, ends in -u. Nouns and adjectives have two cases: nominative for grammatical subjects and in general, and accusative for direct objects and (after a preposition) to indicate direction of movement.

Singular nouns used as grammatical subjects end in -o, plural subject nouns in -oj (pronounced [oi̯] like English "oy"). Singular direct object forms end in -on, and plural direct objects with the combination -ojn ([oi̯n]; rhymes with "coin"): -o- indicates that the word is a noun, -j- indicates the plural, and -n indicates the accusative (direct object) case. Adjectives agree with their nouns; their endings are singular subject -a ([a]; rhymes with "ha!"), plural subject -aj ([ai̯], pronounced "eye"), singular object -an, and plural object -ajn ([ai̯n]; rhymes with "fine").

The suffix -n, besides indicating the direct object, is used to indicate movement and a few other things as well.

The six verb inflections consist of three tenses and three moods. They are present tense -as, future tense -os, past tense -is, infinitive mood -i, conditional mood -us and jussive mood -u (used for wishes and commands). Verbs are not marked for person or number. Thus, kanti means "to sing", mi kantas means "I sing", vi kantas means "you sing", and ili kantas means "they sing".

Word order is comparatively free. Adjectives may precede or follow nouns; subjects, verbs and objects may occur in any order. However, the article la "the", demonstratives such as tiu "that" and prepositions (such as ĉe "at") must come before their related nouns. Similarly, the negative ne "not" and conjunctions such as kaj "and" and ke "that" must precede the phrase or clause that they introduce. In copular (A = B) clauses, word order is just as important as in English: "people are animals" is distinguished from "animals are people".

The Hungarian Academy of Sciences has found that Esperanto fulfills all the requirements of a living language.^[74]

The vocabulary, orthography, phonology, and semantics, are all thoroughly European. The vocabulary, for example, draws about two-thirds from Romance and one-third from Germanic languages; the syntax is Romance; and the phonology and semantics are Slavic. The grammar is arguably more European than not, but Claude Piron among others argues that the derivation system is not particularly European, though the inflection is.^[75][76]

Esperanto is frequently accused of being inherently sexist, because the default form of some nouns is masculine while a derived form is used for the feminine, which is said to retain traces of the male-dominated society of late 19th-century Europe of which Esperanto is a product.^[77][78] These nouns are primarily titles and kin terms, such as sinjoro "Mr, sir" vs. sinjorino "Ms, lady" and patro "father" vs. patrino "mother". In addition, nouns that denote persons and whose definitions are not explicitly male are often assumed to be male unless explicitly made female, such as doktoro, a PhD doctor (male or unspecified) versus doktorino, a female PhD. This is analogous to the situation with the English suffix -ess, as in the words baron/baroness, waiter/waitress, etc. Esperanto pronouns are similar. The pronoun li "he" may be used generically, whereas ŝi "she" is always female.^[79]

Esperanto typically has 22 to 24 consonants, depending on the phonemic analysis and individual speaker, five vowels, and two semivowels that combine with the vowels to form six diphthongs. (The consonant /j/ and semivowel /i̯/ are both written j, and the uncommon consonant /dz/ is written with the digraph dz,^[80] which is the only consonant that doesn't have its own letter.) Tone is not used to distinguish meanings of words. Stress is always on the second-last vowel in fully Esperanto words unless a final vowel o is elided, which occurs mostly in poetry. For example, familio "family" is [fa.mi.ˈli.o], with the stress on the second i, but when the word is used without the final o (famili’), the stress remains on the second i: [fa.mi.ˈli].

The 23 consonants are:

The sound /r/ is usually an alveolar trill [r], but can also be a uvular trill [ʀ],^[81] a uvular fricative [ʁ],^[82] and an alveolar approximant [ɹ].^[83] Many other forms such an alveolar tap [ɾ] are done and accepted in practice. The /v/ is normally pronounced like English v, but may be pronounced [ʋ] (between English v and w) or [w], depending on the language background of the speaker. A semivowel /u̯/ normally occurs only in diphthongs after the vowels /a/ and /e/, not as a consonant /w/. Common, if debated, assimilation includes the pronunciation of nk as [ŋk] and kz as [ɡz].

A large number of consonant clusters can occur, up to three in initial position (as in stranga, "strange") and four in medial position (as in instrui, "teach"). Final clusters are uncommon except in foreign names, poetic elision of final o, and a very few basic words such as cent "hundred" and post "after".

Esperanto has the five vowels found in such languages as Classical Latin, Japanese, Spanish, Swahili, Modern Hebrew, and Modern Greek.

There are also two semivowels, /i̯/ and /u̯/, which combine with the monophthongs to form six falling diphthongs: aj, ej, oj, uj, aŭ, and eŭ.

Since there are only five vowels, a good deal of variation in pronunciation is tolerated. For instance, e commonly ranges from [e] (French é) to [ɛ] (French è). These details often depend on the speaker's native language. A glottal stop may occur between adjacent vowels in some people's speech, especially when the two vowels are the same, as in heroo "hero" ([he.ˈro.o] or [he.ˈro.ʔo]) and praavo "great-grandfather" ([pra.ˈa.vo] or [pra.ˈʔa.vo]).

The following short extract gives an idea of the character of Esperanto.^[84] (Pronunciation is covered above; the Esperanto letter j is pronounced like English y.)

Below are listed some useful Esperanto words and phrases along with IPA transcriptions:

The core vocabulary of Esperanto was defined by Lingvo internacia, published by Zamenhof in 1887. This book listed 900 roots; these could be expanded into tens of thousands of words using prefixes, suffixes, and compounding. In 1894, Zamenhof published the first Esperanto dictionary, Universala Vortaro, which had a larger set of roots. The rules of the language allowed speakers to borrow new roots as needed; it was recommended, however, that speakers use most international forms and then derive related meanings from these.

Since then, many words have been borrowed, primarily (but not solely) from the European languages. Not all proposed borrowings become widespread, but many do, especially technical and scientific terms. Terms for everyday use, on the other hand, are more likely to be derived from existing roots; komputilo "computer", for instance, is formed from the verb komputi "compute" and the suffix -ilo "tool". Words are also calqued; that is, words acquire new meanings based on usage in other languages. For example, the word muso "mouse" has acquired the meaning of a computer mouse from its usage in English. Esperanto speakers often debate about whether a particular borrowing is justified or whether meaning can be expressed by deriving from or extending the meaning of existing words.

Some compounds and formed words in Esperanto are not entirely straightforward; for example, eldoni, literally "give out", means "publish", paralleling the usage of certain European languages (such as German). In addition, the suffix -um- has no defined meaning; words using the suffix must be learned separately (such as dekstren "to the right" and dekstrumen "clockwise").

There are not many idiomatic or slang words in Esperanto, as these forms of speech tend to make international communication difficult—working against Esperanto's main goal.

Instead of derivations of Esperanto roots, new roots are taken from European languages in the endeavor to create an international language.^[85]

Esperanto speakers learn the language through self-directed study, online tutorials, and correspondence courses taught by volunteers. More recently, free teaching websites, like lernu! and Duolingo, are available.

Esperanto instruction is rarely available at schools, including four primary schools in a pilot project under the supervision of the University of Manchester, and by one count at a few universities.^[86] However, outside China and Hungary, these mostly involve informal arrangements rather than dedicated departments or state sponsorship. Eötvös Loránd University in Budapest had a department of Interlinguistics and Esperanto from 1966 to 2004, after which time instruction moved to vocational colleges; there are state examinations for Esperanto instructors.^[87][88] Additionally, Adam Mickiewicz University in Poland offers a diploma in Interlinguistics.^[89] The Senate of Brazil passed a bill in 2009 that would make Esperanto an optional part of the curriculum in public schools, although mandatory if there is demand for it. As of 2015 the bill is still under consideration by the Chamber of Deputies.^[90][91][92]

In the United States, Esperanto is notably offered as a weekly evening course at Stanford University's Bechtel International Center. Conversational Esperanto, The International Language, is a free drop-in class that is open to Stanford students and the general public on campus during the academic year.^[93] With administrative permission, Stanford Students can take the class for two credits a quarter through the Linguistics Department. "Even four lessons are enough to get more than just the basics," the Esperanto at Stanford website reads.

After taking the Esperanto course at their university and becoming fascinated with the language, two Stanford students embarked on a research project travelling around Europe to document the history and usage of Esperanto. They visited formal institutions devoted to Esperanto, including the Esperanto Museum in Vienna, and participated in tours conducted in the language and distributed a survey to major Esperanto organizations. Their research focused on the community of Esperanto speakers with the hope of engaging the Esperanto community and the public at large.^[94]

Various educators have estimated that Esperanto can be learned in anywhere from one quarter to one twentieth the amount of time required for other languages.^[95] Claude Piron, an Esperanto-Activist and Chinese–English–Russian–Spanish translator for the United Nations, argued that Esperanto is far more intuitive than many ethnic languages: "Esperanto relies entirely on innate reflexes [and] differs from all other languages in that you can always trust your natural tendency to generalize patterns. ... The same neuropsychological law [—called by] Jean Piaget generalizing assimilation—applies to word formation as well as to grammar."^[96]

The Institute of Cybernetic Pedagogy at Paderborn University (Germany) has compared the length of study time it takes natively French-speaking high-school students to obtain comparable 'standard' levels in Esperanto, English, German, and Italian.^[97] The results were:

Four primary schools in Britain, with 230 pupils, are currently following a course in "propaedeutic Esperanto"—that is, instruction in Esperanto to raise language awareness and accelerate subsequent learning of foreign languages—under the supervision of the University of Manchester. As they put it,

Studies have been conducted in New Zealand,^[99] United States,^{[100][101][102]} (Germany),^[103] Italy^[104] and Australia.^[105] The results of these studies were favorable and demonstrated that studying Esperanto before another foreign language expedites the acquisition of the other, natural language. This appears to be because learning subsequent foreign languages is easier than learning one's first foreign language, whereas the use of a grammatically simple and culturally flexible auxiliary language like Esperanto lessens the first-language learning hurdle. In one study,^[106] a group of European secondary school students studied Esperanto for one year, then French for three years, and ended up with a significantly better command of French than a control group, who studied French for all four years.

Esperanto is by far the most widely spoken constructed language in the world.^[107] Speakers are most numerous in Europe and East Asia, especially in urban areas, where they often form Esperanto clubs.^[108] Esperanto is particularly prevalent in the northern and central countries of Europe; in China, Korea, Japan, and Iran within Asia;^[45] in Brazil, Argentina, and Mexico in the Americas;^[5] and in Togo in Africa.^[109]

Countering a common criticism against Esperanto, the statistician Svend Nielsen has found there to be no significant correlation between the number of Esperanto speakers and similarity of a given national mother language to Esperanto. He concludes that Esperanto tends to be more popular in countries that are rich, with widespread Internet access and that tend to contribute more to science and culture. Linguistic diversity within a country was found to have a slight inverse correlation with Esperanto popularity.^[110]

An estimate of the number of Esperanto speakers was made by Sidney S. Culbert, a retired psychology professor at the University of Washington and a longtime Esperantist, who tracked down and tested Esperanto speakers in sample areas in dozens of countries over a period of twenty years. Culbert concluded that between one and two million people speak Esperanto at Foreign Service Level 3, "professionally proficient" (able to communicate moderately complex ideas without hesitation, and to follow speeches, radio broadcasts, etc.).^[111] Culbert's estimate was not made for Esperanto alone, but formed part of his listing of estimates for all languages of more than one million speakers, published annually in the World Almanac and Book of Facts. Culbert's most detailed account of his methodology is found in a 1989 letter to David Wolff.^[112] Since Culbert never published detailed intermediate results for particular countries and regions, it is difficult to independently gauge the accuracy of his results.

In the Almanac, his estimates for numbers of language speakers were rounded to the nearest million, thus the number for Esperanto speakers is shown as two million. This latter figure appears in Ethnologue. Assuming that this figure is accurate, that means that about 0.03% of the world's population speak the language. Although it is not Zamenhof's goal of a universal language, it still represents a level of popularity unmatched by any other constructed language.

Marcus Sikosek (now Ziko van Dijk) has challenged this figure of 1.6 million as exaggerated. He estimated that even if Esperanto speakers were evenly distributed, assuming one million Esperanto speakers worldwide would lead one to expect about 180 in the city of Cologne. Van Dijk finds only 30 fluent speakers in that city, and similarly smaller-than-expected figures in several other places thought to have a larger-than-average concentration of Esperanto speakers. He also notes that there are a total of about 20,000 members of the various Esperanto organizations (other estimates are higher). Though there are undoubtedly many Esperanto speakers who are not members of any Esperanto organization, he thinks it unlikely that there are fifty times more speakers than organization members.^[108]

Finnish linguist Jouko Lindstedt, an expert on native-born Esperanto speakers, presented the following scheme^[113] to show the overall proportions of language capabilities within the Esperanto community:

In 2017, doctoral student Svend Nielsen estimated around 63,000 Esperanto speakers worldwide, taking into account association memberships, user-generated data from Esperanto websites and census statistics. This number, however, was disputed by statistician Sten Johansson, who questioned the reliability of the source data and highlighted a wide margin of error, the latter point with which Nielsen agrees. Both have stated, however, that this new number is likely more realistic than some earlier projections.^[4]

In the absence of Dr. Culbert's detailed sampling data, or any other census data, it is impossible to state the number of speakers with certainty. According to the website of the World Esperanto Association:

Native Esperanto speakers, denaskuloj, have learned the language from birth from Esperanto-speaking parents.^[114] This usually happens when Esperanto is the chief or only common language in an international family, but sometimes occurs in a family of Esperanto speakers who often use the language.^[115] The 15th edition of Ethnologue cited estimates that there were 200 to 2000 native speakers in 1996,^[116] but these figures were removed from the 16th and 17th editions.^[117] The current online version of Ethnologue gives "L1 users: 1,000 (Corsetti et al 2004)".^[118] As of 1996, there were approximately 350 attested cases of families with native Esperanto speakers (which means there were around 700 Esperanto speaking natives in these families, not calculating older native speakers).^[119]

Esperantists can access an international culture, including a large body of original as well as translated literature. There are more than 25,000 Esperanto books, both originals and translations, as well as several regularly distributed Esperanto magazines. In 2013 a museum about Esperanto opened in China.^[120] Esperantists use the language for free accommodations with Esperantists in 92 countries using the Pasporta Servo or to develop pen pals through Esperanto Koresponda Servo.^[121]

Every year, Esperantists meet for the World Congress of Esperanto (Universala Kongreso de Esperanto).^[122][123]

Historically, much Esperanto music, such as Kaj Tiel Plu, has been in various folk traditions.^[124] There is also a variety of classical and semi-classical choral music, both original and translated, as well as large ensemble music that includes voices singing Esperanto texts. Lou Harrison, who incorporated styles and instruments from many world cultures in his music, used Esperanto titles and/or texts in several of his works, most notably La Koro-Sutro (1973). David Gaines used Esperanto poems as well as an excerpt from a speech by Dr. Zamenhof for his Symphony No. One (Esperanto) for mezzo-soprano and orchestra (1994–98). He wrote original Esperanto text for his Povas plori mi ne plu (I Can Cry No Longer) for unaccompanied SATB choir (1994).

There are also shared traditions, such as Zamenhof Day, and shared behaviour patterns. Esperantists speak primarily in Esperanto at international Esperanto meetings.

Detractors of Esperanto occasionally criticize it as "having no culture". Proponents, such as Prof. Humphrey Tonkin of the University of Hartford, observe that Esperanto is "culturally neutral by design, as it was intended to be a facilitator between cultures, not to be the carrier of any one national culture". The late Scottish Esperanto author William Auld wrote extensively on the subject, arguing that Esperanto is "the expression of a common human culture, unencumbered by national frontiers. Thus it is considered a culture on its own."^[125]

A number of Esperanto associations also advance education in and about the international language Esperanto and aim to preserve and promote the culture and heritage of Esperanto.^[126] Poland added Esperanto to its list of Intangible heritage in 2014.^[127]

Some authors of works in Esperanto are:

Esperanto has been used in a number of films and novels. Typically, this is done either to add the exotic flavour of a foreign language without representing any particular ethnicity, or to avoid going to the trouble of inventing a new language. The Charlie Chaplin film The Great Dictator (1940) showed Jewish ghetto shop signs in Esperanto. Two full-length feature films have been produced with dialogue entirely in Esperanto: Angoroj, in 1964, and Incubus, a 1965 B-movie horror film which is also notable for starring William Shatner shortly before he began working on Star Trek. In Captain Fantastic (2016) there is a dialogue in Esperanto. Finally, film director Alfonso Cuarón has publicly shown his fascination for Esperanto^[128] and called his production company Esperanto Filmoj ("Esperanto movies").

A language school teaching "Entrenationo" (representing a satire on Esperanto) is featured in Graham Greene's novel The Confidential Agent, which was made into a film starring Charles Boyer and Lauren Bacall (1945). Other amateur productions have been made, such as a dramatization of the novel Gerda Malaperis (Gerda Has Disappeared). In Stamboul Train, Greene used Esperanto as the language on signs at the main train station in Budapest. A number of mainstream films in national languages have used Esperanto in some way.

Esperanto is used as the universal language in the far future of Harry Harrison's Stainless Steel Rat and Deathworld stories. Poul Anderson's story "High Treason" takes place in a future where Earth became united politically but was still divided into many languages and cultures, and Esperanto became the language of its space armed forces, fighting wars with various extraterrestrial races. Esperanto is said to be the official language of all the peoples of Philip José Farmer's Riverworld series.

The opening song to the popular video game Final Fantasy XI, "Memoro de la Ŝtono", was written in Esperanto. It was the first game in the series that was played online, and would have players from both Japan and North America (official European support was added after the North American launch) playing together on the same servers, using an auto-translate tool to communicate. The composer, Nobuo Uematsu, felt that Esperanto was a good language to symbolize worldwide unity.

In the geek fiction novel Off to Be the Wizard, Esperanto is programmed as the language that triggers all of the wizard's spells. A teacher explains that this is because "no one really speaks Esperanto and it's easy to learn".

Esperanto is found in the Image Comics series Saga as the language Blue, spoken by the horned inhabitants of Wreath. It is rendered in blue-colored text. Blue is generally only spoken by inhabitants of Wreath, while most other cultures use a universal language that appears to be simply named "Language." Some Wreath inhabitants use translator rings to communicate with those who don't speak Blue. Magic seems to be activated via the linguistic medium of Blue.

In the television show Red Dwarf, which begins in the late 22nd century, crewman Arnold Rimmer constantly spends his time trying to learn Esperanto and failing, even compared to his bunkmate Dave Lister who only maintains a casual interest. Additionally many of the signs around the ship Red Dwarf are written in both English and Esperanto. The novel Infinity Welcomes Careful Drivers states that, although not required, it is widely expected that officers in the Space Corps be fluent in the language, hence Rimmer's interest.

Esperanto is available in the language selection in the video game Minecraft.^[129]

In Season 1, episode 15 of Nickelodeon's Danny Phantom the Werewolf-type creature, Wulf, speaks in Esperanto.

In the 2010 animated film Superman/Batman: Apocalypse Supergirl is heard speaking Esperanto. It is never referred to as Esperanto, and serves as a proxy for the language of Krypton.

In 1921 the French Academy of Sciences recommended using Esperanto for international scientific communication.^[130] A few scientists and mathematicians, such as Maurice Fréchet (mathematics), John C. Wells (linguistics), Helmar Frank (pedagogy and cybernetics), and Nobel laureate Reinhard Selten (economics) have published part of their work in Esperanto. Frank and Selten were among the founders of the International Academy of Sciences in San Marino, sometimes called the "Esperanto University", where Esperanto is the primary language of teaching and administration.^[131][132]

A message in Esperanto was recorded and included in Voyager 1's Golden Record.

Esperanto business groups have been active for many years. The French Chamber of Commerce did research in the 1920s and reported in The New York Times in 1921 that Esperanto seemed to be the best business language.^[133]

Zamenhof had three goals, as he wrote already in 1887: to create an easy language, to create a language ready to use "whether the language be universally accepted or not" and to find some means to get many people learn the language.^[20] So Zamenhof's intention was not only to create an easy-to-learn language to foster peace and international understanding as a general language, but also to create a language for immediate use by a (small) language community. Esperanto was to serve as an international auxiliary language, that is, as a universal second language, not to replace ethnic languages. This goal was widely shared among Esperanto speakers in the early decades of the movement. Later, Esperanto speakers began to see the language and the culture that had grown up around it as ends in themselves, even if Esperanto is never adopted by the United Nations or other international organizations.^[130]

Esperanto speakers who want to see Esperanto adopted officially or on a large scale worldwide are commonly called finvenkistoj, from fina venko, meaning "final victory".^[134] It has to be noted that there are two kinds of "finvenkismo"–"desubismo" and "desuprismo"; the first aims to spread Esperanto between ordinary people ("desube", from below) aiming to form a steadily growing community of Esperanto speakers. The second aims to act from above ("desupre"), beginning with politicians. Zamenhof considered the first way to have a better perspective, as "for such affairs as ours, governments come with their approval and help usually only, when everything is already completely finished".^[135]

Those who focus on the intrinsic value of the language are commonly called raŭmistoj, from Rauma, Finland, where a declaration on the short-term improbability of the fina venko and the value of Esperanto culture was made at the International Youth Congress in 1980.^[136] However the "Manifesto de Raŭmo" clearly mentions the intention to further spread the language: "We want to spread Esperanto to put into effect its positive values more and more, step by step".^[137]

In 1996 the Prague Manifesto was adopted at the annual congress of the World Esperanto Association (UEA); it was subscribed by individual participants and later by other Esperanto speakers. More recently, language-learning apps like Duolingo and Amikumu have helped to increase the amount of fluent speakers of Esperanto, and find others in their area to speak the language with.

The earliest flag, and the one most commonly used today, features a green five-pointed star against a white canton, upon a field of green. It was proposed to Zamenhof by Richard Geoghegan, author of the first Esperanto textbook for English speakers, in 1887. The flag was approved in 1905 by delegates to the first conference of Esperantists at Boulogne-sur-Mer. A version with an "E" superimposed over the green star is sometimes seen. Other variants include that for Christian Esperantists, with a white Christian cross superimposed upon the green star, and that for Leftists, with the color of the field changed from green to red.^[138]

In 1987, a second flag design was chosen in a contest organized by the UEA celebrating the first centennial of the language. It featured a white background with two stylised curved "E"s facing each other. Dubbed the "jubilea simbolo" (jubilee symbol),^[139] it attracted criticism from some Esperantists, who dubbed it the "melono" (melon) because of the design's elliptical shape. It is still in use, though to a lesser degree than the traditional symbol, known as the "verda stelo" (green star).^[140]

Esperanto has been placed in many proposed political situations. The most popular of these is the Europe–Democracy–Esperanto, which aims to establish Esperanto as the official language of the European Union. Grin's Report, published in 2005 by François Grin, found that the use of English as the lingua franca within the European Union costs billions annually and significantly benefits English-speaking countries financially.^[141] The report considered a scenario where Esperanto would be the lingua franca, and found that it would have many advantages, particularly economically speaking, as well as ideologically.

Russian Esperanto writer Nikolai Nekrasov was arrested during the Stalinist repressions of the late 1930s, accused of being "an organizer and leader of a fascist, espionage, terrorist organization of Esperantists", and executed on October 4, 1938. Another Esperanto writer Vladimir Varankin was executed on October 3, 1938.

Esperanto has served an important role in several religions, such as Oomoto from Japan and the Bahá'í Faith from Iran, and has been encouraged by others, like some Spiritist movements.

The Oomoto religion encourages the use of Esperanto among its followers and includes Zamenhof as one of its deified spirits.^[142]

The Bahá'í Faith encourages the use of an auxiliary international language. `Abdu'l-Bahá praised the ideal of Esperanto, and there was an affinity between Esperantists and Bahá'ís during the late 19th century and early 20th century.^[143][144]

On February 12, 1913, `Abdu'l-Bahá gave a talk to the Paris Esperanto Society,

Lidia Zamenhof, daughter of L. L. Zamenhof, became a Bahá'í around 1925.^[144] James Ferdinand Morton, Jr., an early member of the Bahá'í Faith in Greater Boston, was vice-president of the Esperanto League for North America.^[146] Ehsan Yarshater, the founding editor of Encyclopædia Iranica, notes how as a child in Iran he learned Esperanto and that when his mother was visiting Haifa on a Bahá'í pilgrimage he wrote her a letter in Persian as well as Esperanto.^[147] At the request of 'Abdu’l-Baha, Agnes Baldwin Alexander became an early advocate of Esperanto and used it to spread the Bahá’í teachings at meetings and conferences in Japan.

Today there exists an active sub-community of Bahá'í Esperantists and various volumes of Bahá'í literature have been translated into Esperanto. In 1973, the Bahá'í Esperanto-League for active Bahá'í supporters of Esperanto was founded.^[144]

In 1908, spiritist Camilo Chaigneau wrote an article named "Spiritism and Esperanto" in the periodic La Vie d'Outre-Tombe recommending the use of Esperanto in a "central magazine" for all spiritists and esperantists. Esperanto then became actively promoted by spiritists, at least in Brazil, initially by Ismael Gomes Braga and František Lorenz; the latter is known in Brazil as Francisco Valdomiro Lorenz, and was a pioneer of both spiritist and Esperantist movements in this country.^[148]

The Brazilian Spiritist Federation publishes Esperanto coursebooks, translations of Spiritism's basic books, and encourages Spiritists to become Esperantists.^[149]

The first translation of the Bible into Esperanto was a translation of the Tanakh or Old Testament done by L. L. Zamenhof. The translation was reviewed and compared with other languages' translations by a group of British clergy and scholars before its publication at the British and Foreign Bible Society in 1910. In 1926 this was published along with a New Testament translation, in an edition commonly called the "Londona Biblio". In the 1960s, the Internacia Asocio de Bibliistoj kaj Orientalistoj tried to organize a new, ecumenical Esperanto Bible version.^[150] Since then, the Dutch Remonstrant pastor Gerrit Berveling has translated the Deuterocanonical or apocryphal books in addition to new translations of the Gospels, some of the New Testament epistles, and some books of the Tanakh or Old Testament. These have been published in various separate booklets, or serialized in Dia Regno, but the Deuterocanonical books have appeared in recent editions of the Londona Biblio.

Christian Esperanto organizations include two that were formed early in the history of Esperanto:

Individual churches using Esperanto include:

Ayatollah Khomeini of Iran called on Muslims to learn Esperanto and praised its use as a medium for better understanding among peoples of different religious backgrounds. After he suggested that Esperanto replace English as an international lingua franca, it began to be used in the seminaries of Qom. An Esperanto translation of the Qur'an was published by the state shortly thereafter.^[161][162]

Though Esperanto itself has changed little since the publication of Fundamento de Esperanto (Foundation of Esperanto), a number of reform projects have been proposed over the years, starting with Zamenhof's proposals in 1894 and Ido in 1907. Several later constructed languages, such as Universal, were based on Esperanto.

In modern times, attempts have been made to eliminate perceived sexism in the language, such as Riism.

There are some geographical and astronomical features named after Esperanto, or after its creator L. L. Zamenhof. These include Esperanto Island in Antarctica,^[163] and the asteroids 1421 Esperanto and 1462 Zamenhof discovered by Finnish astronomer and Esperantist Yrjö Väisälä.