- Gess is played on a grid of 18 × 18 ''squares''.
- Two players, "Black" and "White", each have 43 stones of their colour on the board in the starting configuration.
- Starting with Black, players take turns moving a piece on the board.
- A ''piece'' consists of a 3 × 3 grid of squares around a central square, each of which is occupied only by stones of one colour (or not occupied). The central square identifies the piece, and must exist on the board; the surrounding squares may be off the edge of the board (in which case they are unoccupied).
- Each piece can move as determined by the stones in its 3 × 3 grid, termed the ''footprint'' of the piece:
- --- The central square determines the extent of the piece's movement. If the square is unoccupied, it may move up to three spaces; if it is occupied by a stone, it may move any number of spaces.
- --- Each of the eight surrounding squares determines the directions the piece can move. If a square has a stone, the piece can move in the direction indicated by the square's location relative to the central square; if a square is unoccupied, the piece cannot move in that direction.
- As a piece moves, all of the stones in its footprint move in unison.
- When the footprint of a piece coincides with any other stones on the board, those stones are removed from the board and the move ends.
- A ''ring'' is any piece consisting of eight stones around an empty central square.
- When, at the end of any turn, a player has no ring pieces on the board, that player loses the game.
- The game object is to be the only player with a ring piece on the board.
A Go set is one easy way to assemble the equipment needed for gess. The 19 × 19 line grid is simultaneously an 18 × 18 grid of squares, and the starting position needs only 43 each of the black and white stones.
The rules describe a highly variable set of pieces, which will often change every turn. In total there are 510 possible sets of a ''footprint''; however, the starting position uses these rules to emulate , Queen , Bishop , Rook and Pawn in this order R - B - Q - K - B - R in the last row (black's view) and 6 pawns in the next row.
The game objective, to remove the opponent's "ring" (described as a piece that moves like a chess king) also mimics that of chess.
The rows are named 2 to 19 (1 and 20 being outside the grid), and the files are named ''b'' to ''s'' (''a'' and ''t'' again being outside the grid).
A move is notated by noting the place of the centre of the footprint at the beginning of a move and its place at the end of the move.
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