Description logic (DL) is a family of formal knowledge representation languages. It is more expressive than propositional logic but has more efficient decision problems than first-order predicate logic.

DL is used in artificial intelligence for formal reasoning on the concepts of an application domain (known as terminological knowledge). It is of particular importance in providing a logical formalism for ontologies and the Semantic Web. The most notable application outside information science is in bioinformatics where DL assists in the codification of medical knowledge.