Definition:
From 1948 to 1993, the FIDE Interzonal tournament was the second stage of the qualifying cycle for the World Chess Championship. The participants were successful players from preliminary zonal tournaments plus unsuccessful players from the third stage of the preceding cycle. The successful players in the Interzonal qualified into the third stage of the cycle, the Candidates' tournament.
From 1948 to 1970, the Interzonal was a single round robin tournament. From 1973 to 1979, two tournaments were held, and from 1982 to 1987, three tournaments were held. The last two Interzonals, in 1990 and 1993, were Swiss Systems.
In 1997 and afterwards, the Interzonal was replaced by the World Championship Knockout (elimination) tournament.
