Interzonal chess tournaments were tournaments organized by FIDE, the World Chess Federation, and were a stage in the triennial World Chess Championship cycle.

In the first year of the cycle, every FIDE member nation would hold a national championship, with the top players qualifying for the Zonal tournament. The world was divided into distinct zones, with the USSR, United States and Canada each being designated a zone, thus qualifiers from these three zones went directly to the Interzonal. Smaller countries would be grouped into a zone with many countries. For example, all of South America and Central America combined originally formed one zone.

Players who won their Zonal tournaments, and who had scored above a prescribed level, typically received at least title norms towards international chess titles, such as International Master and Grandmaster; sometimes, winners could receive these titles outright, depending upon the strength of the zone.

The top players in each Zonal tournament would meet in the Interzonal tournament, which would typically have between 20 and 24 players. The top finishers (e.g., the top six in 1958) would qualify for the Candidates Tournament, which would take place the following year. They would be joined in the Candidates by the loser of the previous candidates' final and the loser of the previous world championship match. 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.

John van der Wiel (born 9 August 1959) is a Dutch chess grandmaster. He was awarded the Grandmaster title in 1982.

He was the European Junior Champion in 1978 and the champion of the Netherlands in 1986. He was a participant in the Chess Olympiads of 1980, 1982 and 1984. He has competed in several interzonal tournaments: Moscow (1982) where he finished in 11th - 12th place, and Biel (1985) 4th - 6th place (where he lost a playoff for the final Candidates Tournament place to Nigel Short). His best results in the other international tournaments have included Sochi (1980) - 4th - 5th place; Wijk aan Zee (1981, additional tournament) 1st place; Wijk aan Zee (1982) 3rd - 4th; and Novi Sad (1982). In the past, he was a notable "computer killer".

Garry Kimovich Kasparov (Russian: Га́рри Ки́мович Каспа́ров, Russian pronunciation: [ˈɡarʲɪ ˈkʲiməvʲɪtɕ kɐˈsparəf]; born Garik Kimovich Weinstein, 13 April 1963) is a Russian (formerly Soviet) chess grandmaster, a former World Chess Champion, writer, political activist, considered by many to be the greatest chess player of all time.

Kasparov became the youngest ever undisputed World Chess Champion in 1985 at the age of 22 by defeating then-champion Anatoly Karpov. He held the official FIDE world title until 1993, when a dispute with FIDE led him to set up a rival organization, the Professional Chess Association. He continued to hold the "Classical" World Chess Championship until his defeat by Vladimir Kramnik in 2000. He was the first world champion to lose a match to a computer under standard time controls, when he lost to Deep Blue in 1997.

Kasparov's ratings achievements include being rated world No. 1 according to Elo rating almost continuously from 1986 until his retirement in 2005 and holding the all-time highest rating of 2851. He was the world No. 1 ranked player for 255 months, by far the most of all-time and nearly three times as long as his closest rival, Anatoly Karpov. Kasparov also holds records for consecutive tournament victories and Chess Oscars.

Robert James "Bobby" Fischer (March 9, 1943 – January 17, 2008) was an American chess Grandmaster and the 11th World Chess Champion. He is widely considered one of the greatest chess players of all time. Fischer was also a best-selling chess author. After ending his competitive career, he proposed a new variant of chess and a modified chess timing system. His idea of adding a time increment after each move is now standard, and his variant Chess960 is gaining in popularity.

A chess prodigy, at age 13 Fischer won a "brilliancy" that became known as The Game of the Century. Starting at age 14, he played in eight United States Championships, winning each by at least a point. At age 15½, he became both the youngest grandmaster and the youngest candidate for the World Championship up to that time. He won the 1963–64 U.S. Championship 11–0, the only perfect score in the history of the tournament. In the early 1970s he became one of the most dominant players in modern history—winning the 1970 Interzonal by a record 3½-point margin and winning 20 consecutive games, including two unprecedented 6–0 sweeps in the Candidates Matches. According to research by Jeff Sonas, in 1971 Fischer had separated himself from the rest of the world by a larger margin of playing skill than any player since the 1870s. He became the first official World Chess Federation (FIDE) number-one rated chess player in July 1971, and his 54 total months at number one is the third longest of all time.

Mikhail Tal (Latvian: Mihails Tāls; Russian: Михаил Нехемьевич Таль, Michail Nechem'evič Tal, [mʲixʌˈiɫ nʲɪˈxɛmʲɪvʲit͡ɕ ˈtal]; sometimes transliterated Mihails Tals or Mihail Tal; November 9, 1936 – June 28, 1992) was a Soviet-Latvian chess Grandmaster and the eighth World Chess Champion.

Widely regarded as a creative genius, and the best attacking player of all time, he played in a daring, combinational style. His play was known above all for improvisation and unpredictability. Every game, he once said, was as inimitable and invaluable as a poem. He was often called "Misha", a diminutive for Mikhail, and "The magician from Riga". Both The Mammoth Book of the World's Greatest Chess Games (Burgess, Nunn & Emms 2004) and Modern Chess Brilliancies (Evans 1970) include more games by Tal than any other player. Tal was also a highly-regarded chess writer.

He holds the records for both the first and second longest unbeaten streaks in competitive chess history. Many authorities consider him to have been the greatest attacking Grandmaster in the history of chess. On May 28, 1992, dying from kidney failure, he left hospital to play at the Moscow blitz tournament, where he defeated Garry Kasparov. He died one month later. The Mikhail Tal Memorial is held in Moscow each year since 2006 to honour his memory.