Book excerpt: This book constitutes the proceedings of the 9th International Workshop on Enterprise and Organizational Modeling and Simulation, EOMAS 2013, held in conjunction with CAiSE 2013 in Valencia, Spain, in June 2013. Tools and methods for modeling and simulation are widely used in enterprise engineering, organizational studies and business process management. In monitoring and evaluating business processes and the interactions of actors in a realistic environment, modeling and simulation have proven to be both powerful, efficient and economic, especially if complemented by animation and gaming elements. The ten contributions in this volume were carefully reviewed and selected from 22 submissions. They explore the above topics, address the underlying challenges find and improve solutions, and show the application of modeling and simulation in the domains of enterprises, their organizations and underlying business processes.