The Nimzo-Indian is an extremely popular and reliable defence, upon which most world champions have relied at some point in their careers. Black controls the vital e4-square with his pieces, and retains total flexibility with his central pawns. By playing 4 f3, White challenges Black's idea head-on. Either Black grants White control of e4, or else he must commit his pawn to d5, whereupon White can begin concrete action in the centre. The result is sharp, forcing play of a type that is rare in the early stages of most Nimzo-Indians. 4 f3 is an excellent choice for ambitious players who are willing to prepare carefully, as it can be used to steamroller opponents who have not worked out an accurate response. The 4 f3 Nimzo enjoyed a period of great popularity in the early 1990s, following a number of spectacular victories by the teenage Alexei Shirov. However, good responses were found and the line's popularity declined. A number of players quietly worked away at revitalizing 4 f3, and it is now once again a potent weapon. Following its period out of the limelight, it has now regained its surprise value, which will be greatly valued by club players wishing to spring 4 f3 on their opponents. Yuri Yakovich is an experienced grandmaster and renowned trainer from the Russian city of Samara. His numerous tournament victories include three consecutive triumphs at Santo Antonio during 1999-2001. Yakovich has played the 4 f3 Nimzo-Indian frequently during his career, and has made important contributions to its theory.