This volume contains the papers presentedat the 20th InternationalConference onLogicProgramming,held in Saint-Malo,France,September 6-10,2004.Since the ?rst meeting in this series, held in Marseilles in 1982, ICLP has been the premier international conference for presenting research in logic programming. This year, we received 70 technical papers from countries all over the world, and the ProgramCommittee accepted 28 of them for presentation;they are included in this volume. A stand-by-your-postersession took place during the conference. It servedas aforumforpresentingworkinamoreinformalandinteractivesetting.Abstracts ofthe16postersselectedbytheProgramCommitteeareincludedinthisvolume as well. The conference program also included invited talks and invited tutorials. We were privileged to have talks by three outstanding researchers and excellent speakers: Nachum Dershowitz (Tel Aviv University, Israel) talked on Ter- nation by Abstraction, Michael Gelfond (Texas Tech University, USA) on - swer Set Programming and the Design of Deliberative Agents,andG' erard Huet (INRIA, France) on Non-determinism Lessons. Two of the invited talks appear in these proceedings.The tutorials covered topics of high interest to the logic programming community: Ilkka Niemel. a gave a tutorial on The Implementation of Answer Set Solvers, Andreas PodelskionTree Automata in Program Analysis and Veri?cation, and Guillermo R. Simari onDefeasible Logic Programming and Belief Revision. Satelliteworkshopsmadetheconferenceevenmoreinteresting.Sixworkshops collocated with ICLP 2004: - CICLOPS2004, Colloquium on Implementation of Constraint and Logic Programming Systems, organized by Manuel Carro. - COLOPS2004,2ndInternationalWorkshoponConstraint&LogicProgr- ming in Security, organized by Frank Valencia. - MultiCPL2004, 3rd International Workshop on Multiparadigm Constraint, organized by Petra Hofstedt. - TeachLP2004,1stInternationalWorkshoponTeachingLogicProgramming, organized by Dietmar Seipel.

This volume contains the papers presentedat the 20th InternationalConference onLogicProgramming,held in Saint-Malo,France,September 6-10,2004.Since the ?rst meeting in this series, held in Marseilles in 1982, ICLP has been the premier international conference for presenting research in logic programming. This year, we received 70 technical papers from countries all over the world, and the ProgramCommittee accepted 28 of them for presentation;they are included in this volume. A stand-by-your-postersession took place during the conference. It servedas aforumforpresentingworkinamoreinformalandinteractivesetting.Abstracts ofthe16postersselectedbytheProgramCommitteeareincludedinthisvolume as well. The conference program also included invited talks and invited tutorials. We were privileged to have talks by three outstanding researchers and excellent speakers: Nachum Dershowitz (Tel Aviv University, Israel) talked on Ter- nation by Abstraction, Michael Gelfond (Texas Tech University, USA) on - swer Set Programming and the Design of Deliberative Agents,andG' erard Huet (INRIA, France) on Non-determinism Lessons. Two of the invited talks appear in these proceedings.The tutorials covered topics of high interest to the logic programming community: Ilkka Niemel. a gave a tutorial on The Implementation of Answer Set Solvers, Andreas PodelskionTree Automata in Program Analysis and Veri?cation, and Guillermo R. Simari onDefeasible Logic Programming and Belief Revision. Satelliteworkshopsmadetheconferenceevenmoreinteresting.Sixworkshops collocated with ICLP 2004: - CICLOPS2004, Colloquium on Implementation of Constraint and Logic Programming Systems, organized by Manuel Carro. - COLOPS2004,2ndInternationalWorkshoponConstraint&LogicProgr- ming in Security, organized by Frank Valencia. - MultiCPL2004, 3rd International Workshop on Multiparadigm Constraint, organized by Petra Hofstedt. - TeachLP2004,1stInternationalWorkshoponTeachingLogicProgramming, organized by Dietmar Seipel.