This is a completely revised and rewritten edition of the 1983 book by the same authors. Since the earlier edition the Petroff has been enriched by the introduction of many new tactical variations, often involving castling on opposite sides, which make it an ideal weapon for the counter-attacking player. All the important variations are covered in depth with many new suggestions and improvements by the two authors, but there are still many unexplored areas for those with adventurous ideas.