The United Nations International School (UNIS) is a private international school in New York City which was established in 1947. Many members of the United Nations staff arriving with young families found unexpected difficulties with the school system in New York. Among them was K. T. Behanan and his wife, who arrived from India in May 1947 with their five-year-old son to help the UN's Trusteeship Council with educational policy. The Behanans banded together with other UN families who were in a similar situation to establish the United Nations International School at Lake Success, with Dr. Behanan as chairman of its board. The school was founded to provide an international education for students, while preserving its students' diverse cultural heritages. Today, UNIS has over 1,600 students in one campus in Manhattan, close to the Headquarters of the United Nations. The Manhattan campus, overlooking the East River, is K-12; until 2022, the school also ran a K-8 school at a campus in Jamaica Estates, Queens.

UNIS was one of the pilot schools of the International Baccalaureate (IB) and was among those awarding the first IB diplomas. The comprehensive K–12 curriculum prepares UNIS students for the IB, and the school's internationally recognized academic standards attempts to enable students to go on to study in top colleges/universities both in the United States and the rest of the world.

The main language used in the school is English, and all students study either French or Spanish from Kindergarten to the 12th Grade. Arabic, French, Chinese, German, Italian, Japanese and Russian are also taught beginning in the 7th Grade, where students are required to decide one of the seven languages to pursue further along with "Language A" English and "Language B" French or Spanish (Language C is Arabic, French, Chinese, German, Italian, Japanese, or Spanish). Students can also choose French or Spanish again for Language C, and must pursue the Language C until the 12th Grade. Additional languages can be studied by students within and external to the school during the weekend or after school during the school week. The school's current executive director is Dr. Dan Brenner.

UNIS is a member of the Council of International Schools, the International Baccalaureate Organization, the European Council of International Schools, the New York State Association of Independent Schools, the National Association of Independent Schools and the College Board along with being registered to the New York Board of Regents as an independent, not-for-profit school.

In the formative years, UNIS offers a school-designed curriculum, from Kindergarten (JA, in UNIS) to the 12th Grade (T4), in which elementary school (junior school, in UNIS), middle school and high school (tut house) students enroll for the International Baccalaureate Diploma (IBDP) or IB Courses, where a wide range of subjects are offered. Within the framework of IB requirements, students have the possibility to choose from over two-hundred course combinations.

Students are taught in relatively small classes, with averages of 17 children in Kindergarten, 17 in the 1st Grade (J1), 17 in the 2nd Grade (J2), 19 in Grades 3–4 (J3-J4) and 21 throughout middle and high school (M1-T4). Emphasis is placed on preparation for the IB exams during high school, for which virtually all seniors sit (full Diploma or Certificate). Children whose parents transfer from abroad to work for the United Nations, Missions to the United Nations, and Consulates enjoy priority in terms of admission, but admission is not automatic. All children are required to be interviewed and assessed in-person at UNIS, in addition to consideration of official school reports, if any.

The AEFE categorizes this school as a French international school.

Nearly all UNIS graduates matriculate at four-year colleges in the semester following graduation, with a small number choosing a gap-year program. A typical year will see 75% to 85% of graduates enrolling at colleges in the United States, with remaining graduates attending 20 different universities in thirteen countries outside the U.S.