This book constitutes the refereed proceedings of the 23rd International Conference on Logic Programming, ICLP 2007, held in Porto, Portugal, September 8-13, 2007.

The 22 revised full papers together with 2 invited talks as well as 15 poster presentations and the abstracts of 5 doctoral consortium articles were carefully reviewed and selected from 74 initial submissions. The papers cover all issues of current research in logic programming - they are organized in topical sections on theory, functional and constraint logic programming, program analysis, answer-set programming, semantics, and applications.

The papers in this collection were presented at the 7th International Con- rence on Logic Programming and Nonmonotonic Reasoning (LPNMR-7) in Fort Lauderdale, Florida, USA, during January 6-8, 2004. The previous meetings in this series were held in Washington, DC, USA (1991), Lisbon, Portugal (1993), Lexington, USA (1995), Dagstuhl, Germany (1997), El Paso, USA (1999), and Vienna, Austria (2001). LPNMR conferences are a forum for exchanging ideas on declarative logic programming, nonmonotonic reasoning and knowledge representation. In the 1980sresearchersworkingintheareaofnonmonotonicreasoningdiscoveredthat their formalisms could be used to describe the behavior of negation as failure in Prolog, andthe?rstLPNMRmeetingwasconvenedforthepurposeofdiscussing thisrelationship.Thisworkhasledtothecreationoflogicprogrammingsystems of a new kind, answer set solvers, and to the emergence of a new approach to solving combinatorial search problems, called answer set programming. The highlights of LPNMR-7 were three invited talks, given by Rina Dechter (University of California, Irvine), Henry Kautz (University of Washington) and Torsten Schaub (University of Potsdam). The program also included 24 regular papers selected after a rigorous review process, 8 system descriptions, and 2 panels. We would like to thank the Program Committee members and additional reviewers for careful, unbiased evaluation of the submitted papers. We are also grateful to Paolo Ferraris for help with publicizing the Call for Papers, to Fred Ho?man for help with local organizational matters, and to Matti J] arvisalo for help with the organization of the electronic Program Committee meeting."