The game of Experthello is played on an 8 by 8 board. There are 64 markers which have contrasting colors on their opposite sides. Initially the first four markers are placed diagonally in the central four squares.
The players place markers on the board in unoccupied squares. Each marker must be placed so that it is adjacent to an enemy marker, either orthogonally or diagonally. In addition, the marker must be placed in line with a friendly marker and separated from it by one or more enemy markers (and no empty spaces). All enemy markers so flanked are reversed. Markers remain fixed during a game, but a marker may be reversed any number of times. If the placing of the marker simultaneously captures two or more chains of enemy markers, the markers in all captured chains are reversed.
Pieces may be captured only by the placing of a marker. Enemy markers flanked at both ends as the result of other causes are not captured. If a player cannot make a legal move he loses his turn. He continues to lose his turn until a legal move becomes possible for him.
The game ends when all 64 squares are filled, or when neither player can move. The winner is the player with the most markers on the board.