Portal:Chess/Selected article/Introduction/Chess opening
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A chess opening is the group of initial moves of a chess game (the opening moves). Recognized sequences of opening moves are referred to as openings as initiated by White or defenses, as created in reply by Black. There are many dozens of different openings, and hundreds of named variants. The Oxford Companion to Chess lists 1327 named openings and variants. These vary widely in character from quiet positional play (e.g. the Réti Opening and some lines of the Queen's Gambit Declined) to wild tactical play (e.g. the Latvian Gambit and Two Knights Defense, particularly the Traxler Variation).
A sequence of opening moves that is considered standard (often cataloged in a reference work such as the Encyclopedia of Chess Openings) is referred to as "the book moves", or simply "book". These reference works often present these move sequences in simple algebraic notation, opening trees, or theory tables. A new sequence of moves in the opening is referred to as a "theoretical novelty"; such "prepared variations" can be a formidable weapon in top-class competition. When a game begins to deviate from known opening theory, the players are said to be "out of book". In some opening lines, the moves considered best for both sides have been worked out for twenty to twenty-five moves or more. Professional chessplayers spend years studying openings, and continue doing so throughout their careers, as opening theory continues to evolve.
