Classification of chess openings

The beginning chess position offers White twenty possible first moves.

Of these, 1.e4, 1.d4, 1.Nf3, and 1.c4 are by far the most popular as these moves do the most to promote rapid development and control of the center. A few other opening moves are considered reasonable but less consistent with opening principles than the four most popular moves.

The Dunst Opening, 1.Nc3, develops a knight to a good square, but is somewhat inflexible because it blocks White's c-pawn; also, after 1...d5 the knight is liable to be driven to an inferior square by ...d4. (Note that after 1.Nf3 the analogous 1...e5? loses a pawn.)

Bird's Opening, 1.f4, addresses center control but not development and weakens the king position slightly.

The Sokolsky Opening 1.b4 and the King's and Queen's fianchettos: Larsen's Opening 1.b3 and 1.g3 aid development a bit, but they only address center control peripherally and are slower than the more popular openings.

The eleven remaining possibilities are rarely played at the top levels of chess. Of these, the best are merely slow such as 1.c3, 1.d3, and 1.e3. Worse possibilities either ignore the center and development such as 1.a3, weaken White's position (for instance, 1.f3 and 1.g4), or place the knights on poor squares (1.Na3 and 1.Nh3).

Black has twenty possible responses to White's opening move. Many of these are mirror images of the most popular first moves for White, but with one less tempo. Defenses beginning with 1...c6 and 1...e6, often followed by the center thrust 2...d5, are also popular. Defenses with an early ...d6 coupled with a kingside fianchetto are also commonly played.

The most important scheme of classifying chess openings for serious players is by ECO code, a series of 500 opening codes assigned by the Encyclopaedia of Chess Openings. Although these codes are invaluable for the serious study of the chess opening, they are not very practical for a broad survey of the chess opening as the codes obscure common structural features between related openings.