Logic Programming and Nonmonotonic Reasoning : 5th International Conference LPNMR’ 99 El Paso Texas USA December 2–4 1999 Proceedings This book constitutes the refereed proceedings of the 5th International Conference on Logic Programming and Nonmonotonic Reasoning LPNMR 99 held in El Paso Texas USA in December 1999. The volume presents 26 contributed papers and four invited talks three appearing as extended abstracts and one as a full paper. Topics covered include logic programming non monotonic reasoning knowledge representation semantics complexity expressive power and implementation and applicatons