This book constitutes the refereed proceedings of the 6th International Conference on Logic Programming and Nonmonotonic Reasoning, LPNMR 2001, held in Vienna, Austria in September 2001. The 22 revised full papers and eleven system descriptions presented with five invited papers were carefully reviewed and rigorously selected. Among the topics addressed are computational logic, declarative information extraction, model checking, inductive logic programming, default theories, stable logic programming, program semantics, incomplete information processing, concept learning, declarative specification, Prolog programming, many-valued logics, etc.