John Caius, also known as Johannes Caius and Ioannes Caius, was an English physician, and second founder of Gonville and Caius College, Cambridge.

Gonville and Caius College, often referred to simply as Caius, is a constituent college of the University of Cambridge in Cambridge, England. Founded in 1348 by Edmund Gonville, it is the fourth-oldest of the University of Cambridge's 31 colleges and one of the wealthiest. In 1557, it was refounded by alumnus John Caius. The college has been attended by many students who have gone on to significant accomplishment, including fifteen Nobel Prize winners, the second highest of any Oxbridge college.