[1] The extent of the arrangement differs from case to case, but commonly includes the right to dine at one's sister college, the right to book accommodation there, the holding of joint events between JCRs and invitations to May balls.
Most of the pairings reflect similarities between the two colleges concerned, often parallel histories.
For example, University College, Oxford (an ancient and prestigious college, founded 1249) is paired with Trinity Hall, Cambridge (of equivalent reputation, founded 1350).
The two Colleges both share distinguished choral reputations.
[3] While Oriel and Clare share a common founding year of 1326 and a long history of association, in the 1980s the newly coeducational Clare associated with the then female-only St. Hugh's to protest against Oriel's remaining all male.