An Assistant Language Teacher (ALT) is a foreign national serving as an assistant teacher (paraprofessional educator) in a classroom in Japan, particularly for English as a second language.

The role was created by the Japanese Ministry of Education at the time of the creation of the JET Programme as a translation of the term 外国語指導助手 (gaikokugo shidō joshu) or literally "foreign language instruction assistant". The terms AET (Assistant English Teacher), ELT (English Language Teacher) and NESA (Native English Speaking Assistant) are also in use. The term is used by the Ministry of Education, local Boards of Education (BOE) and schools in Japan primarily to refer to English language speakers who assist with teaching of English in elementary, junior high and senior high schools. However, some ALTs help teach languages other than English.

ALTs are typically required to be university graduates, but they are usually not certified teachers like their Japanese colleagues. In addition to a degree, ALTs are also required to either be native English speakers, or provide proof of learning the language for a specified period of time, usually at least five years.

The JET Programme set the general prerequisites imposed by Japanese immigration (bachelor's degree, health, nationality) and the characteristics that can be considered to be sought by the Japanese government, boards of education (BOEs), and schools.

In the case of ALTs from private language teaching companies, further requirements may include items such as TEFL certification, Japanese language ability (at least spoken) at a communicative level, teaching experience (both within Japan and in other countries) and other specialized skills (foreign languages other than English, IT, etc.) However, as a basic rule, the standards that are expected of JET Programme are still considered as norms among private language teaching companies that provide ALTs to BOEs, although agreements between BOEs and private companies often allow for a relaxing on some of these rules.

At one time, the majority of ALTs were recruited through the JET Programme, but now most are hired by private language teaching companies, also known as "dispatch companies", either within Japan or abroad. Once hired, ALTs are sent to work in junior and senior high-schools and, increasingly, in elementary schools throughout Japan. ALTs are either assigned to one main school, or can work at a number of different schools in their area. ALTs entering on the JET programme are not required to have any prior teaching experience or ESL training. Many ALTs hired privately have prior experience and/or training.

ALTs hired on the JET Programme typically enter either in July or August, but most private ALTs are usually on a contract which runs from April until at least the end of the third school term in March. Some AETs dispatched to City of Nagoya public schools have contracts that begin in mid-May and end in mid-February. Some ALTs also have set, paid holidays during the spring, summer and winter school vacations, in addition to all Japanese public holidays, but some ALTs are not paid between semesters or for national holidays, and do not receive paid vacation leave. By combining the 23 national holidays with the time off during school holidays, the actual number of working days per year is somewhere near 200 through private companies, which is one of the major attractions of the ALT position, however many schools require you to undertake other tasks when not teaching, so the actual hours worked are similar to other jobs in Japan. Most JET Programme ALTs are required to work through the school holidays, receiving the 23 national holidays plus annual leave as holiday time.

The pay for a private ALT is usually less than a full-time Eikaiwa teacher and far less than a teacher from the JET Programme (¥3.36 to ¥3.96 million depending on year in the program), with some of the lowest salaries around ¥180,000 per month (¥2.16 million annually).