Trinity College Dublin Students' Union

Trinity College Dublin Students' Union (Irish: Aontas Mac Léinn Choláiste na Tríonóide), often referred to by its abbreviation TCDSU (Irish: AMLCT), is a students' union and the recognised representative body for the students of Trinity College Dublin. Its role is to provide a channel between the students and the authorities of the college, as well as to provide services to those students. TCDSU is a constituent organisation of Aontas na Mac Léinn in Éirinn.

The day-to-day business of the Union is run out of Teach 6, also known as Teach Mandela. The union is led by a team of sabbatical officers with the help of part-time officers, faculty convenors, school convenors and class representatives, alongside a number of permanent staff members. The student body elects a president every spring, who oversees the finances and management of the Union. The president for the 2025/26 academic year was Seán Thim O'Leary, until their resignation at the end of October 2025.