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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 López's 1561 text on chess including details of it. In the 20th century, with the discovery that certain endgames (see below) 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.

The exceptional positions (above) were:

1. Two knights versus a pawn (See Troitsky line)
2. Rook and bishop versus a rook
3. Rook and a rook pawn on its original square, versus a pawn blocking the rook pawn and a bishop on the same color as the opponent's pawn.

In 1928 FIDE enacted rules that in the rook and bishop versus rook endgame, 132 moves were allowed, since it was twice the sixty-six moves that were thought to be required at that time (the actual maximal number of moves needed is 59). In 1952 FIDE revised the law, requiring that players agree to an extension for these positions before the first move is made (Whitaker and Hartleb 1960). FIDE rules allowed seventy-five moves for the rook and bishop versus rook (Müller and Lamprecht 2001:299). Apparently at some point, the rule was changed to one hundred moves for such positions^{[citation needed]}. Later more such positions were found, and in 1992 the rule was changed back to fifty moves for all positions. Many of the longest games on record involve the rook and bishop versus rook endgame, when the rule for more moves was in effect. ^[1]

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.

1. ^ http://www.xs4all.nl/~timkr/records/#Longest%20game

The recgames.pgn file may now be downloaded from this page of Tim Krabbe's site -

http://www.xs4all.nl/~timkr/records/records.htm

•   Karsten Müller and Frank Lamprecht (2001). Fundamental Chess Endings. Gambit Publications. ISBN 1-901983-53-6. 

•   Norman T, Whitaker and Glenn Hartleb (1960). Selected Endings. 

• Filipowicz - Smederevac (1966) game at Chessville - The Mad Aussie's Chess Trivia