The maximum number of sets in a match is five for men and three for women.
Usually the first player to win six games wins a set but if the score becomes five-games-all, one player must be two games ahead to win the set.
So a player must win the set 7-5 or 8-6 or 9-7 and so on.
Until the 1970s, this meant sets could potentially last indefinitely.
But in 1971 the All England Club introduced the tie break rule.
Under this rule, once the score reaches six-games-all (it was originally eight-all but reduced to six in 1979), a tie break is played to decide who wins the set.