This volume contains the proceedings of FroCoS2000, the 3rd International WorkshoponFrontiersofCombiningSystems, heldMarch22 24,2000, inNancy, France. Like its predecessors organized in Munich (1996) and in Amsterdam (1998), FroCoS2000 is intended to o?er a common forum for research activities related to the combination and the integration of systems in the areas of logic, automateddeduction, constraintsolving, declarativeprogramming, andarti?cial intelligence. There were 31 submissions of overall high quality, authored by researchers from countries including Australia, Brasil, Belgium,...