Cardiff Students' Union (CSU, Welsh:Undeb Myfyrwyr Caerdydd) is the Students' Union for Cardiff University and is located in Cardiff, Wales.

Cardiff Students' Union supports over 200 student societies and 60 sports clubs with more than 10,000 members.

The Students' Union is also the recognised voice of students at Cardiff University, joining students in campaigning about the issues important to them. The trading subsidiary of CUSU, Cardiff Union Services Limited, manages a purpose-built facility in the centre of Cardiff and operates cafes, shops, bars and events that help fund CUSU's charitable activities. CUSU is based on Park Place and at the Heath Park campus, employing over 100 permanent staff and 300 student staff.

The Students' Union is a democratic membership organisation. The Students' Union is led by groups such as Elected Officers, Campaign Officers, Student Senate, Scrutiny Committee and NUS delegates.

Elections for these positions are held twice each year:

Full-time elected officers – A group of 7 full-time paid individuals who each have areas of responsibility, from being the Students' Union President to Societies and Sports, the Heath Park campus, Welsh language, and Postgraduate and International students. These officers are elected for a year, and either take a year out of university to do the job or do it after they graduate.

Part-time campaign officers – These are 10 student volunteers who campaign on areas that matter to you alongside their studies. This includes representing student groups such as Women, LGBT+ (Open Place and Trans+ Place), Black and Ethnic Minorities, Estranged Students, International Students, Ethics and the Environment, Disability, Mental Health, Student Parents and Mature Students.

The Elected Officer positions consist of a President and six vice-presidents.