This volume presents the proceedings of the workshop CSL '91(Computer Science Logic) held at the University of Berne,Switzerland, October 7-11, 1991. This was the fifth in aseries of annual workshops on computer sciencelogic (thefirst four are recorded in LNCS volumes 329, 385, 440, and533).The volume contains 33 invited and selected papers on avariety of logical topics in computer science, includingabstract datatypes, bounded theories, complexity results,cut elimination, denotational semantics, infinitary queries,Kleene algebra with recursion, minimal proofs, normal formsin infinite-valued logic, ordinal processes, persistentPetri nets, plausibility logic, program synthesis systems,quantifier hierarchies, semantics of modularization, stablelogic, term rewriting systems, termination of logicprograms, transitive closure logic, variants of resolution,and many others.