The Cambridge Spy Ring was a ring of spies in the United Kingdom, who passed information to the Soviet Union during World War II and was active at least into the early 1950s. Four members of the ring were originally identified: Kim Philby (cryptonym: Stanley), Donald Duart Maclean (cryptonym: Homer), Guy Burgess (cryptonym: Hicks) and Anthony Blunt (cryptonyms: Tony, Johnson). Once jointly known as the Cambridge Four and later as the Cambridge Five, the number increased as more evidence came to light.
The term "Cambridge" refers to the recruitment of the group during their education at the University of Cambridge in the 1930s. Debate surrounds the exact timing of their recruitment by Soviet intelligence; Anthony Blunt claimed that they were not recruited as agents until they had graduated. Blunt, an Honorary Fellow of Trinity College, was several years older than Burgess, Maclean, and Philby; he acted as a talent-spotter and recruiter for most of the group save Burgess.
Several people have been suspected of being additional members of the group; John Cairncross (cryptonym: Liszt) was identified as such by Oleg Gordievsky, although many others have also been accused of membership in the Cambridge ring. Both Blunt and Burgess were members of the Cambridge Apostles, an exclusive and prestigious society based at Trinity and King's Colleges. Cairncross was also an Apostle. Other Apostles accused of having spied for the Soviets include Michael Whitney Straight and Guy Liddell.