This book constitutes the refereed proceedings of the 8th International Conference on Logic Programming and Nonmonotonic Reasoning, LPNMR 2005, held in Diamante, Italy in September 2005.

The 25 revised full papers, 16 revised for the system and application tracks presented together with 3 invited papers were carefully reviewed and selected for presentation. Among the topics addressed are semantics of new and existing languages; relationships between formalisms; complexity and expressive power; LPNMR systems: development of inference algorithms and search heuristics, updates and other operations, uncertainty, and applications in planning, diagnosis, system descriptions, comparisons and evaluations; software engineering, decision making, and other domains; LPNMR languages: extensions by new logical connectives and new inference capabilities, applications in data integration and exchange systems, and methodology of representing knowledge