Efim Petrovich Geller (March 2, 1925 - November 17, 1998) was a Soviet chess player.

He is reckoned to have been among the best ten players in the world for around twenty years. He was awarded the International Master title in 1951, and the International Grandmaster title the following year.

He played in more than twenty Soviet Championships, acheiving good results in many and winning in 1979 and 1955 when, despite losing five games, he finished with 12/19 and then defeated Vassily Smyslov in a playoff match. Among his best results in other tournaments were equal first with Mikhail Botvinnik at Wijk aan Zee 1969 (ahead of Paul Keres), first at Moscow 1975 (ahead of Boris Spassky, Viktor Korchnoi and Tigran Petrosian) and equal first with Vassily Smyslov at Wijk aan Zee 1977.

He reached the later stages of the World Championship several times, most notably finishing just half a point short of playing in the final match when he scored 17/27 at the 1962 Candidates Tournament in Curacao (the event was won by Tigran Petrosian who went on to win the title).

Geller is best remembered today for the tactical ability and original attacking style which characterised the earlier part of his career. In later years he became a more rounded player. He was noted as an openings expert, and acted as second (assistant) to Boris Spassky in the World Championship match of 1972 against Bobby Fischer, later seconding Anatoly Karpov. His books included an autobiography, translated by Bernard Cafferty as Grandmaster Geller at the Chessboard (1969).