Constraint Handling Rules (CHR) is a Concurrency (computer science), declarative programming programming language for developing constraint programming systems. CHR was first created by Thom Frühwirth in 1991.

CHR is not commonly used as a programming language in its own right. Rather, it is used to extend a host language with constraint handling. Possible host languages include Prolog, Java programming language and Haskell programming language. CHR is included in major Prolog implementations, including SICStus and SWI-Prolog.

A CHR program, called a constraint handler , is a set of rules for simplification, propagation and simpagation (simultaneous simplification and propation) of (sets of) constraints.

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