Ataxx (アタックス) is a strategy video game that was published in arcades by The Leland Corporation in 1990. It also appeared the same year as Spot: The Video Game and later as the Microscope Puzzle from the 1993 CD-ROM game The 7th Guest. The game was invented by Dave Crummack and Craig Galley in 1988 and was originally called Infection. It was first programmed on Amiga, Commodore 64, and Atari ST.

Although Ataxx was sold as a video game and not with a physical game board, it can be played with a Reversi set.

Ataxx is an abstract strategy board game that involves play by two parties on a seven-by-seven square grid. The object of the game is for the player to make pieces constitute a majority of the pieces on the board at the end of the game, by converting as many of their opponent's pieces as possible.

Each player begins with two pieces, white and black, for the first player and second player respectively. The game starts with the four pieces on the four corners of the board, with white in the top left and bottom right and black on the other two. White moves first.

During their turn, players move one of their pieces either one or two spaces in any direction. Diagonal distances are equivalent to orthogonal distances, i.e. it is legal to move to a square whose relative position is two squares away both vertically and horizontally. If the destination is adjacent to the source, a new piece is created on the empty departure square. Otherwise the piece on the source moves to the destination. After the move, all of the opponent player's pieces adjacent to the destination square are converted to the color of the moving player. Players must move unless no legal move is possible, in which case they must pass.

The board configuration may be altered by having certain squares filled (not playable by either player), or using different board sizes.

The game ends when all squares have been filled or one of the players has no remaining pieces. The player with the most pieces wins. A draw may occur when the number of squares is even, either from non-playable squares or nonstandard sizes having an even number of squares. Some versions also implement the threefold repetition rule from chess.