Description:This book constitutes the proceedings of the 4th International Workshop on Cooperation and Interoperability, Architecture and Ontology, CIAO!, and the 4th International Workshop on Enterprise and Organizational Modeling and Simulation, EOMAS, held at CAiSE 2008 in Montpellier, France, in June 2008. The 13 papers presented here were carefully selected for inclusion in this book. The scopes of these two workshops are to a large extent complementary, with CIAO! being more focused on the theory and application of enterprise engineering and EOMAS on the methods and tools for modeling and simulation. The papers cover the topics of process modeling, collaboration and interoperability, enterprise architecture, and model transformation and simulation.