The winner of the Candidates tournament would play a 24-game match with the World Champion the following year, and need to win outright to gain the title.
The Interzonal was played in January to March 1962, with the top six players qualifying for the Candidates.
The number of top-level players had grown, with the increasing popularization of chess, and the cost of staging these events had become too great.
It had become impractical to put all of the top players into a round robin tournament, so in 1973 the system was changed to two Interzonals (with the first three in each qualifying for the Candidates).
Further increases in the number of qualifiers led to the Interzonal being staged as a single Swiss system tournament in 1990 and 1993.
The system was dropped altogether from the mid-1990s, being replaced by a series of short, knockout-style matches among qualifiers.