Players take turns placing one disk on an empty square, with their assigned color facing up.

When all playable empty squares are filled, the player with more disks showing in their own color wins the game.

Englishmen Lewis Waterman and John W. Mollett[citation needed] both claim to have invented the game of reversi in 1883, each denouncing the other as a fraud.

Later mention includes an 1895 article in The New York Times, which describes reversi as "something like Go Bang, [...] played with 64 pieces.

[citation needed] A Japanese publication in 1907 titled World Games Rules Complete Collection (世界遊戯法大全) describes the board game reversi with the same rules as Othello where the first four pieces go in the center in a diagonal pattern and the player who cannot make a move simply passes.

[3] The modern version of the game—the most regularly used rule-set, and the one used in international tournaments—is marketed and recognized as Othello (オセロ, osero).

[9] The Japanese game company Tsukuda Original launched Othello in late April 1973 in Japan under Hasegawa's license, which led to an immediate commercial success.

All intellectual property regarding Othello outside Japan is now owned by MegaHouse, the Japanese toy company that acquired Tsukuda Original's successor PalBox.

In common practice over the Internet, opponents agree upon a time-control of, typically, from one to thirty minutes per game per player.

Standard time control in the World Championship is thirty minutes, and this or something close to it is common in over-the-board (as opposed to internet) tournament play generally.

In time-defaulted games, where disk differential is used for tie-breaks in tournaments or for rating purposes, one common over-the-board procedure for the winner of defaulted contests to complete both sides' moves with the greater of the result thereby or one disk difference in the winner's favor being the recorded score.

An alternative recording method not requiring a grid is also in use, where positions on a board are labeled left to right by letters a through h and top to bottom by digits 1 through 8.

This alternate notational scheme is used primarily in verbal discussions or where a linear representation is desirable in print, but may also be permissible as during-game transcription by either or both players.

For example, one procedure that has been used is to permit either player to make corrections going back some fixed number of moves.

[citation needed] The Brightwell Quotient (BQ) is calculated as follows:[20] Good Othello computer programs play very strongly against human opponents.

This is mostly due to difficulties in human look-ahead peculiar to Othello: The interchangeability of the disks and therefore apparent strategic meaninglessness (as opposed to chess pieces for example) makes an evaluation of different moves much harder.

In it, then world champion Hiroshi Inoue, although he would go on to win the tournament, lost a game against the computer program The Moor.

In 1997, the computer Othello program Logistello defeated the reigning human champion, Takeshi Murakami, six games to zero.

When generalizing the game to play on an n×n board, the problem of determining if the first player has a winning move in a given position is PSPACE-complete.