Member of Editorial Board, Journal of Applied Logic (JAL) (since 2003).
Member of Editorial Board, New Generation Computing (since 1998).
Member of Editorial Board, CONSTRAINTS,An International Journal (1996-2008).
Editorial Advisor, Journal of Theory and Practice of Logic Programming (TPLP) (2000-2005).
Editorial Advisor, Journal of Logic Programming (JLP) (1998-2000).
Certified Programs and Proofs 2015, Mumbai, India, January 13-14, 2015
Methods for Modalities 2009, Copenhagen, Denmark, November 12-14, 2009.
CSL 2008, Computer Science Logic 2008, Bertinoro, Italy, September 15-20, 2008.
HLCL'00, 4th International Workshop on High-Level Concurrent Languages, Montreal, Canada, September 20, 2000.
ESOP 2000, European Symposium On Programming, Berlin, Germany, March 28-31, 2000, (Program Chair).
ESOP'99 : European Symposium On Programming, Amsterdam, The Netherlands, 1999.
Third International Conference on Principles and Practice of Constraint Programming (CP97), Schloß Hagenberg, Austria, October 29 - November 1, 1997, (Program Chair).
PLILP'97: 9th International Symposium on Programming Languages, Implementations, Logics, and Programs . Southampton, England, September, 1997.
ESSLLI97: 9th European Summer School in Logic, Language and Information, Aix-en-Provence, France, August 11-22, 1997.
Constraints and Constraint Programming, post-conference workshop, 1996 ASIAN COMPUTING SCIENCE CONFERENCE, Singapore, December 2 - 5, 1996.
INAP-96: The 9th Exhibition and Symposium on Industrial Applications of Prolog , Hino, Tokyo, Japan, October, 16-19, 1996.
PLILP'96: 8th International Symposium on Programming Languages, Implementations, Logics, and Programs . Aachen, Germany, September 25-27, 1996.
CP96: Second International Conference on Principles and Practice of Constraint Programming , Cambridge, Massachusetts, USA, August 19-22, 1996.
CADE-13: Thirteenth International Conference on Automated Deduction , Rutgers University, New Brunswick, New Jersey, USA, 30 July - 3 August, 1996.
PAAM'96: First International Conference and Exhibition on Practical Applications of Intelligent Agents and Multi-agents. , London, 22-23 April 1996.
PACT'96: 2nd International Conference on Practical Applications of Constraint Technology , London, 22-26 April 1996.
WLP'95: 11. Workshop Logische Programmierung , Technische Universität Wien, Wien, Österreich, 27. - 29. September 1995.
CP'95: International Conference on Principles and Practice of Constraint Programming. Marseille, France, September 19-22, 1995.
Kruse'95: International KRUSE Symposium on Knowledge Retrieval, Use, and Storage for Efficiency. University of California, Santa Cruz, CA, August 11-13, 1995.
CCP'95: First International Worshop on Concurrent Constraint Programming. Venice, Italy, May 29--31, 1995.
PASCO'94: First International Symposium on Parallel Symbolic Computation, Linz, Austria, September 26--28, 1994.
LPAR'94: 5th International Conference on Logic Programming and Automated Reasoning, Kiev, Ukraine, July 16--21, 1994.
CADE'94: 12th Conference on Automated Deduction, Nancy, France, June 28--July 1, 1994.
ICLP'94: International Conference on Logic Programming, Genoa, Italy, June 13--18, 1994.
PPCP'94: Second Workshop on Principles and Practice of Constraint Programming, Orcas Island, Washington, USA, May 2--4, 1994.
ILPS'93: International Logic Programming, Symposium, Vancouver, British Columbia, October 26--29, 1993.
ALP'92: Third International Conference on Algebraic and Logic Programming, Volterra, Italien, September 2--4, 1992.
KR'92: Third International Conference on Principles of Knowledge Representation and Reasoning, Cambridge, Massachusetts, October 26--29, 1992.
Symposium on Principles of Hybrid Systems, AAAI Fall Symposium Series, Asilomar, California, November 15--177, 1991.
RTA'91: Fouth International Conference on Rewriting Techniques and Applications, Como, Italy, April 10-12, 1991.
ALP'90: Second International Conference on Algebraic and Logic Programming, Nancy, France, October 1-3, 1990.
Program Chair, Third International Conference on Principles and Practice of Constraint Programming (CP97), Schloß Hagenberg, Austria, October 29 - November 1, 1997.
Co-organizer, 1997 CCL II Workshop (CCL'97), Schloß Dagstuhl, Germany, September 3-5, 1997.
Co-organizer: Workshop on Concurrent Constraint Programming in conjunction with Tenth International Conference on Logic Programming, Budapest, Hungary, June24-25, 1993.
Co-organizer: COMPULOG NET Workshop on Constraint Logic Programming, Marseille, March 17--19, 1993.
CoOrganizer: Theorem Proving and Logic Programming with Constraints, Schlo\3 Dagstuhl, Wadern, 20.--26. Oktober 1991.
Executive Committee of the third European Summer School in Language, Logic and Information, Saarbrücken, 12.--23. August 1991.
Mitglied des Graduiertenkollegs Leistungsgarantien für Rechnersysteme. Seit 2000.
Member of the International Post-Graduate College Language Technology and Cognitive Systems. Since 2001.Member of the Esprit Working Group CCL (Construction of Computational Logics), 1992-1998.
Area Coordinator for Constraint Logic Programming of COMPULOG NET, October 1992 - October 1996.
Member of the Esprit Project ACCLAIM (Advanced Concurrent Constraint Languages: Application, Implementation and Technology), 1992-1995.
Scientific Correspondent of the Esprit Working Group COMPASS, A Comprehensive Algebraic Approach to System Specification and Development, 1989-1996.
Mitglied des Graduiertenkollegs Kognitionswissenschaft. 1992-2000.
Mitglied des Graduiertenkollegs Informatik. 1992-2000.
Mitherausgeber der Reihe ``DISKI -- Dissertationen zur K"unstlichen Intelligenz'', Infix Verlag. 1992-1999.