Ever since Nimzowitsch introduced his flexible, dynamic defence to the queen's pawn, debate has raged over White's best reply. Many variations have been in and out of fashion, but one line in particular has proved an enduring weapon - the sound and solid 4 e3 line, known as the Rubinstein Variation. The 4 e3 Nimzo is extraordinarily rich in strategy. All manner of different central pawn-structures can arise, such as the blocked centre characteristic of the Hubner Variation and a variety of IQP positions. Moreover, in some lines the central tension persists well into the middlegame. The 4 e3 Nimzo provides a stern test of both players' understanding of chess, and so is an ideal choice for those who are looking to win as either colour.