University College Dublin Students' Union is the Students' Union of University College Dublin, and has been an active part of campaigns run by its national equivalent, the Union of Students in Ireland. It was founded in 1975 as the successor of the Student Representative Council and began operations in 1975, under the presidency of Enda Connolly. Its primary role is to represent its members views and defend their interests.

All students of UCD who are studying for a degree or postgraduate diploma of the National University of Ireland are, on registration at the university, members. The Union is funded by a membership fee paid at the same time as the student services levy ("Contribution Fee") at the start of the academic year. In addition to its campaign work the Union also provides some services such as five shops; Belfield FM (radio station); Welfare and Education services such as a second-hand bookshop and Niteline phoneline; and the provision of a full-time Accommodation and Employment Officer. UCDSU has offices in the Student Centre and Library Building in Belfield.

The Union is a constituent organisation of, the Union of Students in Ireland (USI).

In 2012 The Union passed a new Constitution that once again changed its structures to meet the needs of its students.

There will now be 4 Sabbatical officers in the 2013/2014 academic year, A President, a Welfare and Equality officer, an Education officer and a Post Grad Education officer.

They sit on the UCDSU Executive, with the 7 College Convenors and the Irish Language Officer.