The JCR (or Junior Combination Room) is the name given to the community of undergraduate students at Caius. It is also the name for the common room used by the undergraduates.

There are about 550 undergraduate students at Caius and they are represented by the Gonville and Caius Students Union (GCSU). The President of the GCSU, together with the President of the Middle Combination Room (the graduate body), represent the students on the College Council (the main decision-making body in the College). Also, executive members of the GCSU represent the JCR on various College committees. The GCSU has its own website maintained by and run for the undergraduate students. The GCSU is also responsible for many other things, including:

• Orchestrating the JCR parenting-scheme. All first year undergraduates are allocated College 'parents' by the GCSU. These 'parents' give friendly advice on academic and other matters. Usually at least one 'parent' is a 2nd or 3rd year student studying the same subject.
• Organising social events.
• Overseeing the finances of the various College clubs and societies.
• Providing information and advice on welfare, housing, financial issues, exam preparation etc. This advice is in addition to the advice provided by each undergraduate's personal Tutor.
• Liaising with the Cambridge University Students' Union (CUSU) and the National Union of Students (NUS).

Many members of the JCR (and MCR) can be found most evenings in the College Bar (below the dining hall). The GCSU reps are always available to chat to new undergraduates and Caius prides itself on the friendliness of its undergraduate community.