Chigorin made a number of contributions to the theory of chess openings. The most important were the Chigorin Variation of the Ruy Lopez (1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 d6 8.c3 O-O 9.h3 Na5) and the Chigorin Defence to the Queen's Gambit (1.d4 d5 2.c4 Nc6).