Article 4: The act of moving the pieces

4.1	Each move must be made with one hand only.
4.2	Provided that he first expresses his intention (for example by saying „j’adoube“ or “I adjust”), the player having the move may adjust one or more pieces on their squares.
4.3	Except as providedin Article 4.2, if the player having the move deliberately touches on the chessboard:
	a.	one or more of his own pieces, he must move the first piece touched which can be moved
	b.	one or more of his opponent’s pieces, he must capture the first piece touched which can be captured
	c.	one piece of each colour, he must capture the opponent’s piece with his piece or, if this is illegal, move or capture the first piece touched which can be moved or captured. If it is unclear, whether the player’s own piece or his opponent’s was touched first, the player’s own piece shall be considered to have been touched before his opponent’s.
4.4	If a player having the move:
	a.	deliberately touches his king and rook he must castle on that side if it is legal to do so
	b.	deliberately touches a rook and then his king he is not allowed to castle on that side on that move and the situation shall be governed by Article 4.3.a
	c.	intending to castle, touches the king or king and rook at the same time, but castling on that side is illegal, the player must make another legal move with his king (which may include castling on the other side). If the king has no legal move, the player is free to make any legal move
	d.	promotes a pawn, the choice of the piece is finalised, when the piece has touched the square of promotion.
4.5	If none of the pieces touched can be moved or captured, the player may make any legal move.
4.6	When, as a legal move or part of a legal move, a piece has been released on a square, it cannot be moved to another square on this move. The move is then considered to have been made:
	a.	in the case of a capture, when the captured piece has been removed from the chessboard and the player, having placed his own piece on its new square, has released this capturing piece from his hand
	b.	in the case of castling, when the player's hand has released the rook on the square previously crossed by the king. When the player has released the king from his hand, the move is not yet made, but the player no longer has the right to make any move other than castling on that side, if this is legal
	c.	in the case of the promotion of a pawn, when the pawn has been removed from the chessboard and the player's hand has released the new piece after placing it on the promotion square. If the player has released from his hand the pawn that has reached the promotion square, the move is not yet made, but the player no longer has the right to play the pawn to another square.
	The move is called legal when all the relevant requirements of Article 3 have been fulfilled. If the move is not legal, another move shall be made instead as per Article 4.5.
4.7	A player forfeits his right to a claim against his opponent’s violation of Article 4 once he deliberately touches a piece.

Note: This is an excerpt from the FIDE Handbook. For actual handbook click here