In chess, a pure mate is a checkmate position such that the mated king is attacked exactly once, and prevented from moving to any of the adjacent squares in its field for exactly one reason per square. Each of the squares in the mated king's field is attacked or "guarded" by one—and only one—attacking unit, or else a square which is not attacked is occupied by a friendly unit, a unit of the same color as the mated king. Some authors allow that special situations involving double check or pins may also be considered as pure mate.

Pure mates are of interest to chess problem composers for their aesthetic value. In real gameplay, their occurrence is incidental. Nevertheless, several famous games have concluded with a pure mate, including the Immortal Game and the Evergreen Game, both won by Adolf Anderssen; the Peruvian Immortal; and the Game of the Century, an early brilliancy won by Bobby Fischer. Siegbert Tarrasch was fond of pure mates, often pointing them out when they occurred.

Pure mate is one of a few terms used by composers to describe the properties of a checkmate position; related concepts include economical mate, model mate, and ideal mate. An economical mate is a position such that all of the attacker's pieces contribute to the checkmate, with the (optional) exception of the king and the pawns. The model mate and the ideal mate are both stronger forms of pure mate. When a checkmate is both "pure and economical", it is said to be a model mate. When, in a pure mate, all material on the board of either color plays a direct role in the checkmate, it is said to be an ideal mate.

A pure mate is a checkmate position such that each of the squares in the king's field is guarded, attacked, or blocked in exactly one way, while the king itself is attacked exactly once. In practice, this means that for each of the squares in the king's field, there is exactly one reason why the mated king cannot be moved to that square to escape check. Some authors omit the detail that the mated king itself is attacked only once. In his Dictionary of Modern Chess, Byrne J. Horton provided the following definition:

PURE MATE: A mating problem situation in which every square next to the black King is guarded by a single white man or occupied by a black man.

Horton's definition assumes a historical norm in chess problems, in which White is the attacking and mating side, while Black is the mated and losing side. However, the concept of a pure mate is also applicable to positions in which Black is the mating side.

In the Oxford Companion to Chess, David Hooper and Kenneth Whyld gave a more complex definition, allowing for exceptions in the cases of pins and double check:

pure mate, or clean mate, a checkmate that meets the following criteria: unoccupied squares in the king's field are attacked once only; pieces that function as self-blocks are not under attack unless necessarily pinned; and the mating move is not a double check unless this is necessary to prevent the defender from interposing a man or capturing a checking piece.