Kasparov, now aged 46, has been preparing for the clash by training in Norway with teenage prodigy Magnus Carlsen.
Kasparov has described the match as "a ceremonial tournament".
Meanwhile, Karpov, 58, has been sparring with a computer and a group of grandmasters from a base on the Spanish coast.
The Valencia tournament comes 25 years after the two grandmasters - then both representing the Soviet Union - squared off for the first time for the world crown.
Kasparov, now one of Russia's opposition leaders, was only 21 when he took on Karpov, then aged 33, in the 1984 match.
Karpov raced to a 4-0 lead after nine games in the "first to six wins" match, with some experts predicting a 6-0 whitewash.
In all, Karpov and Kasparov have battled in five world title matches
But Kasparov battled on, drawing the next 17 games. He lost game 27, but - after another series of draws - claimed his first victory in game 32.
Kasparov eventually managed to close the gap to 5-3, before the duel was controversially stopped by the then Fide (World Chess Federation) boss Florencio Campomanes on alleged health grounds.
The decision was taken despite both players saying they wanted to continue.
In the 1985 rematch, Kasparov beat Karpov, becoming the youngest world champion and heralding a new era in chess.
In 1993, Kasparov broke away from the Fide to form the Professional Chess Association and play English grandmaster Nigel Short for the world title, claiming his hand was forced by corruption and mismanagement. He was beaten for the world championship by Vladimir Kramnik in 2000.
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