A students' union, student government, student senate, students' association, guild of students or government of student body is a student organization present in many colleges and universities, and has started appearing in some high schools. In higher education, the student union is often accorded its own building on the campus, dedicated to social and organizational activities of the membership. In the United States, student union many times only refers to a physical building owned by the university with the purpose to provide services for students without a governing body also referred to as a student activity center. Outside the United States this refers to a representative body.

Depending on the country: the purpose, assembly, method and implementation of the group might vary. Universally the purpose of students' union or student government is to represent fellow students in some fashion.

In some cases students' unions are run by students, independent of the educational facility. The purpose of these organizations is to represent students both within the institution and externally, including on local and national issues. Students' unions are also responsible for providing a variety of services to students. Depending on the organization's makeup students can get involved in the union by becoming active in a committee, by attending councils and general meetings, or by becoming an elected officer.