The MCR - or Middle Common Room - is a student association or Postgraduate society which is administered and populated by postgraduate students with support from your college.
Typically administered by an MCR committee elected from the postgraduate student body, your college MCR will look after the interests of the postgraduate community in your college.
Most MCRs will also have their own facilities, which often becomes a lively focus for the communal and social life of graduates. Indeed, the MCR will generally act as the social epicentre of the graduate community in college, organising social events throughout the year which may include dinners, formal swaps to other colleges, festive parties and special interest talks and movie nights.
The vast majority of postgraduate members of Cambridge colleges do become members of their MCR - however it should be noted that membership is not compulsory and anyone can waive the rights and privileges of membership.
To find out more information about your college's MCR consult your college website. Often each college's MCR will have their own web resources, information pages or indeed a website of their own so you can stay in the loop with what's going on in college!
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Copyright Sir Cam, University of Cambridge