A World Chess Championship was played between Tigran Petrosian and Boris Spassky in Moscow from April 9 to June 9, 1966.

Since FIDE rules only allowed a maximum of three players from the same nation to qualify from the interzonal, Stein and Bronstein were ineligible.

The sixth and final place in the Candidates Tournament was decided in a 4-game playoff in which Portisch beat Reshevsky 2½–½.

Bobby Fischer, the winner of the previous Interzonal in 1962, declined his invitation, despite qualifying by winning the 1963–64 US Championship.

Two players were seeded directly into the tournament: Mikhail Botvinnik (loser of the last championship match) and Paul Keres (2nd place in the 1962 Candidates).