In chess, a cross-check (or counter-check) is a tactic in which a check is played in response to a check, especially when the original check is blocked by a piece that itself either delivers check or reveals a discovered check from another piece. Sometimes the term is extended to cover cases in which the king moves out of check and reveals a discovered check from another piece (this is also known as a royal check); it does not generally apply to cases where the original checking piece is captured.
The cross-check is an essential tactic in winning some endgames such as those with two queens versus one, or a queen and pawn versus a queen. In these cases, the defense usually tries for a perpetual check and sometimes the stronger side can stop it only by a cross-check.