The Interzonal was introduced by the 1948 FIDE important qualification stage in the determination of the challenger of the world chess champion. FIDE has changed the competition format several times since 1997. The last inter-zonal tournament took place in 1993 in Biel / Bienne instead. A victory in this always very strong field interzonal tournaments was also independent of the later stages of the qualification as a great success in the trophy case of a chess player.
For the inter-zone tournament, the winner of the zone tournaments and pre-qualified players from the previous cycle qualified. A predetermined number of highly ranked players from the Interzonal tournament / the interzonal tournaments qualified for the Candidates Tournament. The winner of the Candidates tournament or later the candidate duels was called challengers and then fought in a match against the reigning world chess champion, who was therefore not involved in these qualifying marathon for the title. Such a cycle lasted (including World Cup competition ) three years.
From 1948 to 1970, there were in each case an inter- zone tournament with 20-24 participating. From 1973 to 1979 there were two interzonal tournaments per cycle with 18 to 20 participants. From 1982 to 1987 there were three Interzonal tournaments per cycle with up to 18 participants. We always played against each.
1990 and 1993, there were the last two interzonal tournaments, both of which were played out in the Swiss system ( Open ) tournaments with 64 or 73 participants.
At times, was a kind of country quota, that is, a restriction such that the maximum could qualify three players from the same country in a Interzone tournament for the next stage of the (mostly top eight ) candidates. Leonid Stein, this was twice undoing.