- different rules for capture, move order, game objective, etc.;
- addition, substitution, or removal of pieces in standard chess (non-standard pieces are known as fairy pieces);
- different chessboard (larger or smaller, non-square board shape, or different intra-board cell shapes such as hexagons).
Just as in traditional chess, chess variants can be played over-the-board (OTB), or by correspondence.
Regional chess games, some of which are older than Western chess, such as chaturanga, shatranj, shogi, and xiangqi, are typically called chess variants in the Western world even though they are not derived from, or inspired by, western chess. They have some similarities to chess and share a common game ancestor.
The number of possible chess variants is extraordinarily huge. Confining the number to published variants, D. B. Pritchard, author of The Encyclopedia of Chess Variants, estimates that there are well over 2,000.
These chess variants are derived from chess by changing the board, board setup, pieces, or rules.
Orthodox chess rules
Many variants employ standard chess rules and mechanics, but vary the starting position of the pieces or number of pieces.
Orthodox rules on a standard 8×8 board
Different starting position
These variants use standard boards and pieces, but the pieces start on nontraditional squares. In most such variants, the pawns are placed on their usual squares, but the position of other pieces is either randomly determined or selected by the players. The motivation for these variants is usually to nullify established opening knowledge. The downside of these variants is that the initial position usually has less harmony and balance than the standard chess position.
- Chess960 (or Fischer Random Chess): The placement of the pieces on the first rank is randomised, with the opponent's pieces mirroring it. Invented by Bobby Fischer (1996).
- Displacement chess: Some pieces in the initial position are exchanged but the rules remain exactly the same. Some examples of this may be that the king and queen are flipped, or the knight on the b-file is traded with the bishop on the f-file.
- Pre-chess: Proposed by Pal Benko in 1978. The game starts with white and black pawns set as usual, but the initial position of other pieces is selected by the players. White first places one of his pieces on his first rank, and then Black does the same. Players continue to alternate in this manner until all pieces have been placed, with the only restriction being that bishops must be on opposite-colour squares. The game then proceeds in the usual way.
- Transcendental chess: Similar to Chess960, but the opening white and black positions do not mirror each other.
- Upside-down chess: The white and black pieces are switched so that White's pieces are on the 8th rank, with pawns on the 7th rank, one step away from promotion. The starting position looks like a standard chess starting position, but from the other player's perspective. As the pawns are blocked by pieces in the starting position, the game always starts with a knight move and smother checkmates are common.
Different number of pieces
These variants use standard chess pieces on a standard board, but players begin with unorthodox numbers of pieces. For example, starting with multiple queens or fewer pawns. Many such games use unbalanced starting positions, with one player having more or less of a particular piece than the other player.
- Charge of the Light Brigade: Apart from the usual king and pawns, one side has three queens and the other has seven knights.
- Dunsany's chess (and the similar Horde chess): One side has standard chess pieces, and the other side has 32 pawns (or 36 in the case of Horde chess).
- Endgame chess (or The Pawns Game): Players start the game with only pawns and a king. Normal check, checkmate, en passant, and pawn promotion rules apply.
- Handicap chess (or Chess with odds): Variations to equalise chances of players with different strength.
- Peasants' Revolt: White has a king and eight pawns (the peasants) against Black's king, pawn, and four knights (the nobles). Black has the advantage. To narrow the contest, the game has also been played with three knights (on b8, c8, and g8) instead of four. By R. L. Frey (1947).
- Sixteen Pawns: White plays without his queen, but chooses where on the third and fourth ranks to place eight extra pawns. By Legall de Kermeur (18th century). Alexandre Deschapelles and Louis-Charles Mahé de La Bourdonnais later established that eight extra pawns favour White too much, and hence played the game with only five, six, or seven extra pawns for White instead.
- Really Bad Chess: A mobile video game by Zach Gage; Each player has one king and fifteen other pieces selected at random.
- Weak!: White has the usual pieces, Black has one king, seven knights, and sixteen pawns. This game was played at a Columbia University chess club in the 1960s.
Orthodox rules on an unorthodox board
In these variants, the same pieces and rules as in chess are used, but the board is different; It can be smaller or larger, the shape of either the board or individual spaces can be non-square or modular, or it can even be extra-dimensional or unbounded. The movement of pieces in some variants is modified in concurrence with the geometry of the gameboard.
- Active Chess: Played on a 9×8 board, adding a queen with an extra pawn in front. Invented by G. Kuzmichov (1989), whose students tested the game, deciding that the optimal starting position was to place the second queen on the eighth or ninth files.
- Balbo's Game: A novel-shaped board with 70 squares. Full armies for each player, minus one pawn. No castling. By G. Balbo (1974).
- Brusky's Hexagonal Chess: Chess on an irregular board of 84 hex cells. Same as Gliński's Hexagonal Chess, but with ten pawns instead of nine, linear startup, two forward move directions for pawns, pawns capture forward diagonally, and castling. By Yakov Brusky (1966).
- Circular chess: Played on a circular board consisting of four rings, each of sixteen squares.
- Cross chess: Cross-shaped cells, board geometry like hex chess but moves akin to normal chess (e.g. bishops have four directions (not six); queens eight (not twelve)). Extra rook, knight, and pawn per side. By George Dekle Sr.
- Cylinder chess: Played on a cylinder board with a- and h-files "connected". Thus a player can use them as if the a-file were next to the h-file (and vice versa).
- De Vasa's Hexagonal Chess: Chess on a rhombus-shaped board of 81 hex cells. Same as Gliński's Hexagonal Chess, but linear startup, two forward move directions for pawns, pawns capture forward diagonally to the side, and castling. Invented by Helge E. de Vasa (1953).
- Double chess: Two full armies per side on a 12×16 board, the first to mate an enemy king wins. Pawns advance up to four steps on their first move. Capablanca found the game "remarkably interesting".
- Doublewide chess: Two regular chessboards are connected (for a 16×8 play surface). Each player plays with two complete sets of chess pieces.
- Flying chess: Played on a board of 8×8×2, giving a total of 128 cells. Only certain pieces can move to and from the additional level.
- Gliński's Hexagonal Chess: The most popular version of chess for the hex board. Includes three bishops, nine pawns, 91 hex cells. Invented by Władysław Gliński (1936).
- Grid chess: The board is overlaid with a grid of lines. For a move to be legal, it must across at least one of these lines.
- Hexagonal chess: A family of variants played on a hexgrid with three colours and three bishops.