In Japan, a junior idol (ジュニアアイドル, junia aidoru), alternatively chidol (チャイドル, chaidoru) or low teen idol (ローティーンアイドル, rōtīn aidoru), is primarily defined as young child pursuing a career as a photographic model. Generally, this means gravure, or "cheesecake", fully clothed shots; but, junior idols can, and some do, eventually enter the AV industry. Child actors, musicians, and J-pop singers (whose musical genre is often termed idol pop) can also be considered junior idols and are often featured in photobooks and image DVDs.

Female fashion models (not to be confused with glamour models, including gravure idols) also begin their careers typically at age 13–15, but are usually not considered junior idols. Child models, whose careers are usually over by their early young years, are also not usually considered junior idols

There exists no clear set of guidelines regarding the age at which an individual becomes a junior idol: Yumi Adachi, for instance, started her modeling career at age two and many other idols have starred in image DVDs at the ages of three, four and five. The majority of junior idols belong to specialized talent agencies, some of which offer acting and voice training and are geared towards the production of television commercials, photobooks, and related materials. Though sources indicate revenue is relatively low for photographic models, a number of idols (and their parents) see this activity as a gateway to more mainstream media roles.^[7] These transitions are indeed frequent, one example being the case of Saaya Irie who was cast into the live action adaptation of the popular anime series Hell Girl

The trend of junior idols dates back to the mid-1990s, a period marked by significant increase in the number of child models and works involving individuals in that age range.^[8] The term chidol, a neologism of the words "child" and "idol", was coined by columnist Akio Nakamori to describe this new phenomena.^[8] Eventually, this term fell out of use and was replaced by "Junior Idol".^[8] Compared to chidol, the term "junior idol" plays down the association with age and lends some credibility to the industry associating it with the legitimate mainstream idol culture in Japan.^[8]

Content is available in many formats, usually physical goods such as bond photobooks, CDs and DVDs, but also digital content in the form of Portable Document Format books, JPEG photo sets, high resolution movie clips, etc. To promote a particular idol, or to celebrate the release of a specific title, certain stores hold special events where fans get to meet the idols, shake hands with them, obtain autographs or take photographs, either polaroids or pictures taken with the customers' own cameras, in accordance with the amount of money spent on related goods (either regular DVDs, photobooks, etc., or multiple copies of the same title).

Concerning the contents of the titles put on sale, these include, in general terms, pictures or footage of the idols trying out a variety of outfits, such as school uniforms, bathing suits, gym clothes, yukata or even maid, police and anime-inspired costumes.

Some services providers, such as Imouto Club (清純いもうと倶楽部, Seijun Imōto Kurabu)—a subscription-based website—also feature short radio and movie dramas, available for download and later purchase on DVD.

The junior idol industry is a highly contentious one in Japan.

Many Japanese criticise such depictions of underaged girls, including some Japanese politicians.^[8] Despite such disapproval, stores selling junior idol-related materials proliferate in prominent areas such as Oimoya, an area located in Japan's well-known Akihabara shopping district.^[8]

Internationally, the junior idol trend has been harshly criticised.

In 2008, the United Nations Children's Fund launched a Say 'NO' to Child Pornography campaign in Japan.^[9] As part of the campaign, four major internet portal site providers in Japan removed junior idol-related content from their services.^[9] The campaign also garnered over 100,000 signatures in a petition to the Japanese government to amend its child pornography laws to criminalise procession of child pornography, including junior idol materials.^[9]

Junior idol materials stand on legally ambiguous ground in Japan.^[10] Regulation of such materials comes under the Japanese Anti-child prostitution and pornography law.^[10]

The Japanese Anti-child prostitution and pornography law was enacted in November 1999—and revised in 2004 to criminalize distribution of child pornography over the Internet—defines child pornography as the depiction "in a way that can be recognized visually, such a pose of a child relating to sexual intercourse or an act similar to sexual intercourse with or by the child", of "a pose of a child relating to the act of touching genital organs, etc." or the depiction of "a pose of a child who is naked totally or partially in order to arouse or stimulate the viewer's sexual desire."^[11]

Despite inherent difficulties in effectively enforcing a ban on such materials, on August 25, 2007 the Japanese branch of Amazon.com removed over 600 junior idol titles on grounds the likelihood these were produced in violation of the Japanese anti-child prostitution and pornography law was high.^[12] This incident was then followed by the arrest—on October 16—of 34-year-old Jisei Arigane (有金慈青), chief producer of Shinkosha (心交社) (a company specialized in idol and pornographic materials, as well as a number of novels and technical texts) and three associates over the production of an "obscene" DVD shot earlier in 2007 in the Indonesian island of Bali, starring a girl who was seventeen at the time. The prolonged filming of the girl's genitalia was in violation of Japanese law.^[13] Following the incident, the release date of several photobooks and DVDs originally slated for publication in November 2007 was postponed and idol events cancelled.