Introduction -- Background -- Sequent Calculus for ALC -- Comparing SCalc with other ALC Deduction Systems -- Natural Deduction for ALC.- A Proof Theory for ALCQI -- Proofs and Explanations -- A Prototype Theorem Prover -- Conclusion.

Description Logics (DLs) is a family of formalisms used to represent knowledge of a domain. They are equipped with a formal logic-based semantics. Knowledge representation systems based on description logics provide various inference capabilities that deduce implicit knowledge from the explicitly represented knowledge. A Proof Theory for Description Logics introduces Sequent Calculi and Natural Deduction for some DLs (ALC, ALCQ). Cut-elimination and Normalization are proved for the calculi. The author argues that such systems can improve the extraction of computational content from DLs proofs for explanation purposes.