The theme of Sovereign Chess is chess on a larger board (16x16) with multiple colors of neutral pieces around the edge of the board.
Each player begins with a normal complement of chess pieces--one player is black, and the other is white. Moves follow that of traditional chess, with a few variations--most notably that pawns may move orthogonally (and capture diagonally) toward the center of the board.
When a player's piece is on a colored square, she controls the pieces of that color. Players can control multiple colors at once, either with a number of their own pieces, or through a "chain" of pieces. For example, if the white player has her pawn on a red square, and then moves a red pawn to the blue square, then she controls both red and blue.
The goal of the game is to checkmate the opposing king.