The Queen's Indian Defence has traditionally been an extremely reliable opening for Black, guaranteeing a solid position. The Kasparov System (4 a3) is an aggressive attempt to cut across Black's plans, invariably leading to dynamic positions with tactical opportunities for both sides. Pioneered by the former World Champion, Tigran Petrosian, this variation received a fresh lease of life in the 1980s following its adoption by Garry Kasparov, who used it to score many scintillating victories during his rise to the chess summit, since when it has remained an important part of his repertoire. Kasparov introduced several new schemes of development, causing a complete reappraisal of the opening by his fellow Grandmasters, which has continued unabated into the 1990s. However, there remain many uncharted waters for enterprising players to explore.