In chess an exchange sacrifice occurs when one player gives up a rook for a minor piece (a knight or bishop). It is often used to destroy the enemy pawn structure (as in several variations of the Sicilian Defence where Black plays RxNc3), to establish a minor piece on a strong square (often threatening the enemy king), to improve one's own pawn structure (creating, for example, connected passed pawns), or to gain time for development. Tigran Petrosian, the world Champion from 1963-1969, was well known for his especially creative use of this device; in the game Reshevsky-Petrosian, Zurich 1953, he sacrificed the exchange on move 25, only for his opponent to sacrifice it in return on move 30 (the game ended in a draw); this game is perhaps the most famous and most frequently taught example of the exchange sacrifice.

The fifty move rule in chess states that a player can claim a draw if no capture has been made and no pawn has been moved in the last fifty consecutive moves. The relevant part of the official FIDE laws of chess is rule 9.3:

The game is drawn, upon a correct claim by the player having the move, if

a. he writes on his scoresheet, and declares to the arbiter his intention to make a move which shall result in the last 50 moves having been made by each player without the movement of any pawn and without the capture of any piece, or

b. the last 50 consecutive moves have been made by each player without the movement of any pawn and without the capture of any piece.

It should be noted that after fifty moves the game is not automatically a draw--the draw must be claimed by the player on move. It is, therefore, possible for a game to continue beyond a point when a draw could be claimed under the rule. Theoretically, a game could legally continue forever, though in practice, when a draw under the fifty-move rule can be claimed, one of the players is usually happy to claim it.

The rule has a long history, with Ruy L�pez' 1561 text on chess including details of it. In the 20th century, with the discovery that certain endgames (such as two bishops and king against knight and king) can only be won in more than fifty moves (without a pawn move or capture) from certain positions, the rule was changed to include certain exceptions in which one hundred moves were allowed with particular material imbalances. The exceptions were later removed and all material combinations are now subject to the fifty move rule.

Games drawn under the fifty move rule before the endgame are rare. One example is Filipowicz - Smederevac, Polanica Zdroj 1966, which was drawn on move 70 without any captures having been made in the whole game and with the last pawn being moved on move 20.