Peterhouse is a constituent college of the University of Cambridge, England. It is the oldest college of the University, having been founded in 1284 by Hugo de Balsham, Bishop of Ely. Peterhouse has 273 undergraduates, 94 full-time graduate students and 45 fellows, making it the smallest of the university's traditional colleges (though larger than some of the colleges which admit only women, graduates, or mature students and which are smaller because of their restricted membership). The modern name of Peterhouse does not include the word "college".

The foundation of Peterhouse dates to 1280, when letters patent from Edward I dated Burgh, Suffolk, 24 December 1280 allowed Hugo de Balsham to keep a number of scholars in the Hospital of St John, where they were to live according to the rules of the scholars of Merton. After disagreement between the scholars and the Brethren of the Hospital, both requested a separation. As a result, in 1284 Balsham transferred the scholars to the present site with the purchase of two houses just outside the then Trumpington Gate to accommodate a Master and fourteen "worthy but impoverished Fellows". The Church of St Peter without Trumpington Gate was to be used by the scholars. Bishop Hugo de Balsham died in 1286, bequeathing 300 marks that were used to buy further land to the south of St Peter's Church, on which the college's Hall was built.