This volume contains the papers presented at the 3rd International Symposium onFoundationsofInformationandKnowledgeSystems(FoIKS2004), whichwas held in Castle Wilhelminenberg, Vienna, Austria, from February 17th to 20th, 2004. FoIKS is a biennial event focussing on theoretical foundations of information and knowledge systems. It aims at bringing together researchers working on the theoretical foundations of information and knowledge systems and attracting researchers working in mathematical ?elds such as discrete mathematics, c- binatorics, logics, and ?nite model theory who are interested in...