Modern Chess Openings

Modern Chess Openings, commonly shortened to MCO, is a series of opening manuals begun in 1911 by R. C. Griffith and J. H. White. Many later editions and revisers turned the title into a durable reference in English-language chess literature.

An opening is the first phase of a game, when both sides develop pieces, contest space, and prepare king safety. A variation is a specific sequence of moves within an opening. MCO presents such sequences compactly, usually as branching alternatives with names, symbols, and short comments. Reading them requires algebraic notation, the fixed-coordinate system that records moves such as e4, Nf3, or Bb5.

The book can help a reader locate a known line, compare replies, and build a repertoire, meaning a prepared set of openings for White and Black. It is not a compulsory script. A move may be established because it has performed well in many games, but the resulting position still has to be understood.

Edition date matters. Opening theory changes as new games and analysis uncover improvements. Modern is part of the historical title, but an old edition does not necessarily describe current best knowledge.