A political party is an organized group of people who have the same ideology, or who otherwise have the same political positions, and who field candidates for elections, in an attempt to get them elected and thereby implement the party's agenda.

While there is some international commonality in the way political parties are recognized and in how they operate, there are often many differences, and some are significant. Many political parties have an ideological core, but some do not, and many represent ideologies very different from their ideology at the time the party was founded. Many countries, such as Germany and India, have several significant political parties, and some nations have one-party systems, such as China and Cuba. The United States is in practice a two-party system but with many smaller parties also participating and a high degree of autonomy for individual candidates.

Political factions have existed in democratic societies since ancient times. Plato writes in his Republic on the formation of political cliques in Classical Athens, and the tendency of Athenian citizens to vote according to factional loyalty rather than for the public good. In the Roman Republic, Polybius coined the term ochlocracy (literally, 'rule of the mob') to describe the tendency of politicians to mobilize popular functionalist sentiment against their political rivals. Factional politics remained a part of Roman political life through the Imperial period and beyond, and the poet Juvenal coined the phrase "bread and circuses" to describe the political class pandering to the citizenry through diversionary entertainments rather than through arguments about policy. "Bread and circuses" survived as part of Byzantine political life - for example, the Nika revolt during the reign of Justinian was a riot between the "Blues" and the "Greens"—two chariot racing factions at the Hippodrome, who received patronage from different Senatorial factions and religious sects. The patricians who sponsored the Blues and the Greens competed with each other to hold ever grander games and public entertainments during electoral campaigns, in order to appeal to the citizenry of Constantinople.

The first modern political factions, however, can be said to have originated in early modern Britain. The first political factions, cohering around a basic, if fluid, set of principles, emerged from the Exclusion Crisis and Glorious Revolution in late 17th century England.^[1] The Whigs supported Protestant constitutional monarchy against absolute rule, they were interested in the citizens of United Kingdom being free from the aristocracy and opposed to any tyranny, however they supported the constitutional aristocracy and does not consider the British nobility abusive because of its limits; the Tories, originating in the Royalist (or "Cavalier") faction of the English Civil War, were conservative royalist supporters of a strong monarchy as a counterbalance to the republican tendencies of Whigs, who were the dominant political faction for most of the first half of the 18th century; the Whigs supported the Hanoverian succession of 1715 against the Jacobite supporters of the deposed Roman Catholic Stuart dynasty, and were able to purge Tory politicians from important government positions after the failed Jacobite rising of 1715. The leader of the Whigs was Robert Walpole, who maintained control of the government in the period 1721–1742; his protege was Henry Pelham (1743–1754).

As the century wore on, the factions slowly began to adopt more coherent political tendencies as the interests of their power bases began to diverge. The Whig party's initial base of support from the great aristocratic families widened to include the emerging industrial interests and wealthy merchants. As well as championing constitutional monarchy with strict limits on the monarch's power, the Whigs adamantly opposed a Catholic king as a threat to liberty,^[2] and believed in extending toleration to nonconformist Protestants, or dissenters. A major influence on the Whigs were the liberal political ideas of John Locke,^[3] and the concepts of universal rights employed by Locke and Algernon Sidney.^[4]

Although the Tories were out of office for half a century, for most of this period (at first under the leadership of Sir William Wyndham) the Tories retained party cohesion, with occasional hopes of regaining office, particularly at the accession of George II (1727) and the downfall of the ministry of Sir Robert Walpole in 1742. They acted as a united, though unavailing, opposition to Whig corruption and scandals. At times they cooperated with the "Opposition Whigs", Whigs who were in opposition to the Whig government; however, the ideological gap between the Tories and the Opposition Whigs prevented them from coalescing as a single party. They finally regained power with the accession of George III in 1760 under Lord Bute.

When they lost power, the old Whig leadership dissolved into a decade of factional chaos with distinct "Grenvillite", "Bedfordite", "Rockinghamite", and "Chathamite" factions successively in power, and all referring to themselves as "Whigs". Out of this chaos, the first distinctive parties emerged. The first such party was the Rockingham Whigs^[5] under the leadership of Charles Watson-Wentworth and the intellectual guidance of the political philosopher Edmund Burke. Burke laid out a philosophy that described the basic framework of the political party as "a body of men united for promoting by their joint endeavours the national interest, upon some particular principle in which they are all agreed". As opposed to the instability of the earlier factions, which were often tied to a particular leader and could disintegrate if removed from power, the party was centred around a set of core principles and remained out of power as a united opposition to government.^[6]

A coalition including the Rockingham Whigs, led by the Earl of Shelburne, took power in 1782, only to collapse after Rockingham's death. The new government, led by the radical politician Charles James Fox in coalition with Lord North, was soon brought down and replaced by William Pitt the Younger in 1783. It was now that a genuine two-party system began to emerge, with Pitt leading the new Tories against a reconstituted "Whig" party led by Fox.^[7][8]

By the time of this split the Whig party was increasingly influenced by the ideas of Adam Smith, founder of classical liberalism. As Wilson and Reill (2004) note, "Adam Smith's theory melded nicely with the liberal political stance of the Whig Party and its middle-class constituents."^[9]

The modern Conservative Party was created out of the 'Pittite' Tories of the early 19th century. In the late 1820s disputes over political reform broke up this grouping. A government led by the Duke of Wellington collapsed amidst dire election results. Following this disaster Robert Peel set about assembling a new coalition of forces. Peel issued the Tamworth Manifesto in 1834 which set out the basic principles of Conservatism – the necessity in specific cases of reform in order to survive, but an opposition to unnecessary change, that could lead to "a perpetual vortex of agitation". Meanwhile, the Whigs, along with free trade Tory followers of Robert Peel, and independent Radicals, formed the Liberal Party under Lord Palmerston in 1859, and transformed into a party of the growing urban middle-class, under the long leadership of William Ewart Gladstone.

Although the framers of the 1787 United States Constitution did not anticipate that American political discourse would become partisan, political controversies in the early 1790s over the extent of federal government powers saw the emergence of two proto-political parties: the Federalist Party and the Democratic-Republican Party, which were championed by Alexander Hamilton and Thomas Jefferson, respectively.^[10][11] However, a consensus reached on these issues ended party politics in 1816 for nearly a decade, a period commonly known as the Era of Good Feelings.^[12]

The splintering of the Democratic-Republican Party in the aftermath of the contentious 1824 presidential election led to the re-emergence of political parties. Two major parties would dominate the political landscape for the next quarter-century: the Democratic Party, led by Andrew Jackson, and the Whig Party, established by Henry Clay from the National Republicans and from other Anti-Jackson groups. When the Whig Party fell apart in the mid-1850s, its position as a major U.S. political party was filled by the Republican Party.

The second half of the 19th century saw the adoption of the party model of politics across Europe. In Germany, France, Austria and elsewhere, the 1848 Revolutions sparked a wave of liberal sentiment and the formation of representative bodies and political parties. The end of the century saw the formation of large socialist parties in Europe, some conforming to the teaching of Karl Marx, others adapting social democracy through the use of reformist and gradualist methods.^[13]

At the same time, the political party reached its modern form, with a membership disciplined through the use of a party whip and the implementation of efficient structures of control. The Home Rule League Party, campaigning for Home Rule for Ireland in the British Parliament was fundamentally changed by the Irish political leader Charles Stewart Parnell in the 1880s. In 1882, he changed his party's name to the Irish Parliamentary Party and created a well-organized grass roots structure, introducing membership to replace "ad hoc" informal groupings. He created a new selection procedure to ensure the professional selection of party candidates committed to taking their seats, and in 1884 he imposed a firm 'party pledge' which obliged MPs to vote as a bloc in parliament on all occasions. The creation of a strict party whip and a formal party structure was unique at the time. His party's efficient structure and control contrasted with the loose rules and flexible informality found in the main British parties; they soon came to model themselves on the Parnellite model.

A political party is typically led by a party leader (the most powerful member and spokesperson representing the party), a party secretary (who maintains the daily work and records of party meetings), party treasurer (who is responsible for membership dues) and party chair (who forms strategies for recruiting and retaining party members, and also chairs party meetings). Most of the above positions are also members of the party executive, the leading organization which sets policy for the entire party at the national level. The structure is far more decentralized in the United States because of the separation of powers, federalism and the multiplicity of economic interests and religious sects. Even state parties are decentralized as county and other local committees are largely independent of state central committees. The national party leader in the U.S. will be the president, if the party holds that office, or a prominent member of Congress in opposition (although a big-state governor may aspire to that role). Officially, each party has a chairman for its national committee who is a prominent spokesman, organizer and fund-raiser, but without the status of prominent elected office holders.

In parliamentary democracies, on a regular, periodic basis, party conferences are held to elect party officers, although snap leadership elections can be called if enough members opt for such. Party conferences are also held in order to affirm party values for members in the coming year. American parties also meet regularly and, again, are more subordinate to elected political leaders.

Depending on the demographic spread of the party membership, party members form local or regional party committees in order to help candidates run for local or regional offices in government. These local party branches reflect the officer positions at the national level.

It is also customary for political party members to form wings for current or prospective party members, most of which fall into the following two categories:

These are useful for party outreach, training and employment. Many young aspiring politicians seek these roles and jobs as stepping stones to their political careers in legislative or executive offices.

The internal structure of political parties has to be democratic in some countries. In Germany Art. 21 Abs. 1 Satz 3 GG establishes a command of inner-party democracy.^[14]

When the party is represented by members in the lower house of parliament, the party leader simultaneously serves as the leader of the parliamentary group of that full party representation; depending on a minimum number of seats held, Westminster-based parties typically allow for leaders to form frontbench teams of senior fellow members of the parliamentary group to serve as critics of aspects of government policy. When a party becomes the largest party not part of the Government, the party's parliamentary group forms the Official Opposition, with Official Opposition frontbench team members often forming the Official Opposition Shadow cabinet. When a party achieves enough seats in an election to form a majority, the party's frontbench becomes the Cabinet of government ministers. They are all elected members. There are members who attend party without promotion.

The freedom to form, declare membership in, or campaign for candidates from a political party is considered a measurement of a state's adherence to liberal democracy as a political value. Regulation of parties may run from a crackdown on or repression of all opposition parties, a norm for authoritarian governments, to the repression of certain parties which hold or promote ideals which run counter to the general ideology of the state's incumbents (or possess membership by-laws which are legally unenforceable).

Furthermore, in the case of far-right, far-left and regionalism parties in the national parliaments of much of the European Union, mainstream political parties may form an informal cordon sanitaire which applies a policy of non-cooperation towards those "Outsider Parties ^[35] " present in the legislature which are viewed as 'anti-system' or otherwise unacceptable for government. Cordons sanitaire, however, have been increasingly abandoned over the past two decades in multi-party democracies as the pressure to construct broad coalitions in order to win elections – along with the increased willingness of outsider parties themselves to participate in government – has led to many such parties entering electoral and government coalitions.^[15]

Starting in the second half of the 20th century, modern democracies have introduced rules for the flow of funds through party coffers, e.g. the Canada Election Act 1976, the PPRA in the U.K. or the FECA in the U.S. Such political finance regimes stipulate a variety of regulations for the transparency of fundraising and expenditure, limit or ban specific kinds of activity and provide public subsidies for party activity, including campaigning.

Partisan style varies according to each jurisdiction, depending on how many parties there are, and how much influence each individual party has.

In a nonpartisan system, no official political parties exist, sometimes reflecting legal restrictions on political parties. In nonpartisan elections, each candidate is eligible for office on his or her own merits. In nonpartisan legislatures, there are no typically formal party alignments within the legislature. The administration of George Washington and the first few sessions of the United States Congress were nonpartisan. Washington also warned against political parties during his Farewell Address.^[16] In the United States, the unicameral legislature of Nebraska is nonpartisan but is elected and often votes on informal party lines. In Canada, the territorial legislatures of the Northwest Territories and Nunavut are nonpartisan. In New Zealand, Tokelau has a nonpartisan parliament. Many city and county governments in the United States and Canada are nonpartisan. Nonpartisan elections and modes of governance are common outside of state institutions.^[17] Unless there are legal prohibitions against political parties, factions within nonpartisan systems often evolve into political parties.

In one-party systems, one political party is legally allowed to hold effective power. Although minor parties may sometimes be allowed, they are legally required to accept the leadership of the dominant party. This party may not always be identical to the government, although sometimes positions within the party may in fact be more important than positions within the government. North Korea and China are examples; others can be found in Fascist states, such as Nazi Germany between 1934 and 1945. The one-party system is thus often equated with dictatorships and tyranny.

In dominant-party systems, opposition parties are allowed, and there may be even a deeply established democratic tradition, but other parties are widely considered to have no real chance of gaining power. Sometimes, political, social and economic circumstances, and public opinion are the reason for others parties' failure. Sometimes, typically in countries with less of an established democratic tradition, it is possible the dominant party will remain in power by using patronage and sometimes by voting fraud. In the latter case, the definition between dominant and one-party system becomes rather blurred. Examples of dominant party systems include the People's Action Party in Singapore, the African National Congress in South Africa, the Cambodian People's Party in Cambodia, the Liberal Democratic Party in Japan, and the National Liberation Front in Algeria. One-party dominant system also existed in Mexico with the Institutional Revolutionary Party until the 1990s, in the southern United States with the Democratic Party from the late 19th century until the 1970s, in Indonesia with the Golkar from the early 1970s until 1998.

Two-party systems are states such as Honduras, Jamaica, Malta, Ghana and the United States in which there are two political parties dominant to such an extent that electoral success under the banner of any other party is almost impossible. One right wing coalition party and one left wing coalition party is the most common ideological breakdown in such a system but in two-party states political parties are traditionally catch all parties which are ideologically broad and inclusive.

The United States has gone through several party systems, each of which has been essentially two-party in nature. The divide has typically been between a conservative and liberal party; presently, the Republican Party and Democratic Party serve these roles. Third parties have seen extremely little electoral success, and successful third party runs typically lead to vote splitting due to the first-past-the-post, winner-takes-all systems used in most US elections. There have been several examples of third parties siphoning votes from major parties, such as Theodore Roosevelt in 1912 and George Wallace in 1968, resulting in the victory of the opposing major party. In presidential elections, the Electoral College system has prevented third party candidates from being competitive, even when they have significant support (such as in 1992). More generally, parties with a broad base of support across regions or among economic and other interest groups have a greater chance of winning the necessary plurality in the U.S.'s largely single-member district, winner-take-all elections.

The UK political system, while technically a multi-party system, has functioned generally as a two-party (sometimes called a "two-and-a-half party") system; since the 1920s the two largest political parties have been the Conservative Party and the Labour Party. Before the Labour Party rose in British politics the Liberal Party was the other major political party along with the Conservatives. Though coalition and minority governments have been an occasional feature of parliamentary politics, the first-past-the-post electoral system used for general elections tends to maintain the dominance of these two parties, though each has in the past century relied upon a third party to deliver a working majority in Parliament.^[18] (A plurality voting system usually leads to a two-party system, a relationship described by Maurice Duverger and known as Duverger's Law.^[19]) There are also numerous other parties that hold or have held a number of seats in Parliament.

Multi-party systems are systems in which more than two parties are represented and elected to public office.

Australia, Canada, Nepal, Pakistan, India, Ireland, United Kingdom and Norway are examples of countries with two strong parties and additional smaller parties that have also obtained representation. The smaller or "third" parties may hold the balance of power in a parliamentary system, and thus may be invited to form a part of a coalition government together with one of the larger parties, or may provide a supply and confidence agreement to the government; or may instead act independently from the dominant parties.

More commonly, in cases where there are three or more parties, no one party is likely to gain power alone, and parties have to work with each other to form coalition governments. This is almost always the case in Germany on national and state level, and in most constituencies at the communal level. Furthermore, since the forming of the Republic of Iceland there has never been a government not led by a coalition, usually involving the Independence Party or the Progressive Party. A similar situation exists in the Republic of Ireland, where no one party has held power on its own since 1989. Since then, numerous coalition governments have been formed. These coalitions have been led exclusively by either Fianna Fáil or Fine Gael.

Political change is often easier with a coalition government than in one-party or two-party dominant systems. If factions in a two-party system are in fundamental disagreement on policy goals, or even principles, they can be slow to make policy changes, which appears to be the case now in the U.S. with power split between Democrats and Republicans. Still coalition governments struggle, sometimes for years, to change policy and often fail altogether, post World War II France and Italy being prime examples. When one party in a two-party system controls all elective branches, however, policy changes can be both swift and significant. Democrats Woodrow Wilson, Franklin Roosevelt and Lyndon Johnson were beneficiaries of such fortuitous circumstances, as were Republicans as far removed in time as Abraham Lincoln and Ronald Reagan. Barack Obama briefly had such an advantage between 2009 and 2011.

Political parties are funded by contributions from

Political parties, still called factions by some, especially those in the governmental apparatus, are lobbied vigorously by organizations, businesses and special interest groups such as trade unions. Money and gifts-in-kind to a party, or its leading members, may be offered as incentives. Such donations are the traditional source of funding for all right-of-centre cadre parties. Starting in the late 19th century these parties were opposed by the newly founded left-of-centre workers' parties. They started a new party type, the mass membership party, and a new source of political fundraising, membership dues.

From the second half of the 20th century on parties which continued to rely on donations or membership subscriptions ran into mounting problems. Along with the increased scrutiny of donations there has been a long-term decline in party memberships in most western democracies which itself places more strains on funding. For example, in the United Kingdom and Australia membership of the two main parties in 2006 is less than an 1/8 of what it was in 1950, despite significant increases in population over that period.

In some parties, such as the post-communist parties of France and Italy or the Sinn Féin party and the Socialist Party, elected representatives (i.e. incumbents) take only the average industrial wage from their salary as a representative, while the rest goes into party coffers. Although these examples may be rare nowadays, "rent-seeking" continues to be a feature of many political parties around the world.^[21]

In the United Kingdom, it has been alleged that peerages have been awarded to contributors to party funds, the benefactors becoming members of the House of Lords and thus being in a position to participate in legislating. Famously, Lloyd George was found to have been selling peerages. To prevent such corruption in the future, Parliament passed the Honours (Prevention of Abuses) Act 1925 into law. Thus the outright sale of peerages and similar honours became a criminal act. However, some benefactors are alleged to have attempted to circumvent this by cloaking their contributions as loans, giving rise to the 'Cash for Peerages' scandal.

Such activities as well as assumed "influence peddling" have given rise to demands that the scale of donations should be capped. As the costs of electioneering escalate, so the demands made on party funds increase. In the UK some politicians are advocating that parties should be funded by the state; a proposition that promises to give rise to interesting debate in a country that was the first to regulate campaign expenses (in 1883).

In many other democracies such subsidies for party activity (in general or just for campaign purposes) have been introduced decades ago. Public financing for parties and/ or candidates (during election times and beyond) has several permutations and is increasingly common. Germany, Sweden, Israel, Canada, Australia, Austria and Spain are cases in point. More recently among others France, Japan, Mexico, the Netherlands and Poland have followed suit.^[22]

There are two broad categories of public funding, direct, which entails a monetary transfer to a party, and indirect, which includes broadcasting time on state media, use of the mail service or supplies. According to the Comparative Data from the ACE Electoral Knowledge Network, out of a sample of over 180 nations, 25% of nations provide no direct or indirect public funding, 58% provide direct public funding and 60% of nations provide indirect public funding.^[23] Some countries provide both direct and indirect public funding to political parties. Funding may be equal for all parties or depend on the results of previous elections or the number of candidates participating in an election.^[24] Frequently parties rely on a mix of private and public funding and are required to disclose their finances to the Election management body.^[25]

In fledgling democracies funding can also be provided by foreign aid. International donors provide financing to political parties in developing countries as a means to promote democracy and good governance. Support can be purely financial or otherwise. Frequently it is provided as capacity development activities including the development of party manifestos, party constitutions and campaigning skills.^[21] Developing links between ideologically linked parties is another common feature of international support for a party.^[21] Sometimes this can be perceived as directly supporting the political aims of a political party, such as the support of the US government to the Georgian party behind the Rose Revolution. Other donors work on a more neutral basis, where multiple donors provide grants in countries accessible by all parties for various aims defined by the recipients.^[21] There have been calls by leading development think-tanks, such as the Overseas Development Institute, to increase support to political parties as part of developing the capacity to deal with the demands of interest-driven donors to improve governance.^[21]

Generally speaking, over the world, political parties associate themselves with colors, primarily for identification, especially for voter recognition during elections.

• Blue generally denotes conservatism.^[26]

• Yellow is often used for liberalism or libertarianism.

• Red often signifies social democratic, socialist or communist parties.

• Green is often associated with green politics, Islamism, agrarianism and Irish republicanism.

• Orange is the traditional color of Christian democracy.

• Black is generally associated with fascist parties, going back to Benito Mussolini's blackshirts, but also with Anarchism. Similarly, brown is sometimes associated with Nazism, going back to the Nazi Party's tan-uniformed storm troopers.

Color associations are useful when it is not desirable to make rigorous links to parties, particularly when coalitions and alliances are formed between political parties and other organizations, for example: "Purple" (Red-Blue) alliances, Red-green alliances, Blue-green alliances, Traffic light coalitions, Pan-green coalitions, and Pan-blue coalitions.

Political color schemes in the United States diverge from international norms. Since 2000, red has become associated with the right-wing Republican Party and blue with the left-wing Democratic Party. However, unlike political color schemes of other countries, the parties did not choose those colors; they were used in news coverage of 2000 election results and ensuing legal battle and caught on in popular usage. Prior to the 2000 election the media typically alternated which color represented which party each presidential election cycle. The color scheme happened to get inordinate attention that year, so the cycle was stopped lest it cause confusion the following election.^[27]

The emblem of socialist parties is often a red rose held in a fist. Communist parties often use a hammer to represent the worker, a sickle to represent the farmer, or both a hammer and a sickle to refer to both at the same time.

The emblem of Nazism, the swastika or "hakenkreuz", has been adopted as a near-universal symbol for almost any organised white supremacist group, even though it dates from more ancient times.

During the 19th and 20th century, many national political parties organized themselves into international organizations along similar policy lines. Notable examples are The Universal Party, International Workingmen's Association (also called the First International), the Socialist International (also called the Second International), the Communist International (also called the Third International), and the Fourth International, as organizations of working class parties, or the Liberal International (yellow), Hizb ut-Tahrir, Christian Democratic International and the International Democrat Union (blue). Organized in Italy in 1945, the International Communist Party, since 1974 headquartered in Florence has sections in six countries. Worldwide green parties have recently established the Global Greens. The Universal Party, The Socialist International, the Liberal International, and the International Democrat Union are all based in London. Some administrations (e.g. Hong Kong) outlaw formal linkages between local and foreign political organizations, effectively outlawing international political parties.

French political scientist Maurice Duverger drew a distinction between "cadre" parties and "mass" parties. Cadre parties were political elites that were concerned with contesting elections and restricted the influence of outsiders, who were only required to assist in election campaigns. Mass parties tried to recruit new members who were a source of party income and were often expected to spread party ideology as well as assist in elections. Socialist parties are examples of mass parties, while the Conservative Party in the UK and the German Christian Democratic Union in Germany are examples of hybrid parties. In the United States, where both major parties were cadre parties, the introduction of primaries and other reforms has transformed them so that power is held by activists who compete over influence and nomination of candidates.^[28]

Klaus von Beyme categorised European parties into nine families, which described most parties. He was able to arrange seven of them from left to right: Communist, Socialist, Green, Liberal, Christian democratic, Conservative and Libertarian. The position of two other types, Agrarian and Regional/Ethnic parties varied.^[29]