Elisa Bertino is professor of Computer Science and Electrical and Computer Engineering, and research director of the Center for Education and Research in Information Assurance and Security (CERIAS) at Purdue University. She has carried out extensive research on various security topics, such as foundations of access control systems, security for location-based applications, security for web services, digital identity management, data privacy, security and privacy for healthcare applications and for GIS; and has given numerous presentations and tutorials on these topics in scientific conferences. Recently, she recently received the IEEE Computer Society 2005 Kanai award for her research in security for distributed systems. She has also served as a member of the Microsoft Trustworthy Computing Academic Advisory Board. Lorenzo D. Martino is visiting assistant professor at the Computer and Information Technology (C&IT) department of Purdue University and at the Cyber Center of the Purdue University. He has carried out research on trust negotiation techniques and security for web services. Federica Maria Francesca Paci is a PhD Student at the University of Milan, Italy. Her main research interests include the development of access control models for constraint workflow systems, Web services access control models and secure distribution of XML documents. She has published several refereed journal and conference papers in these areas. Anna Squicciarini is a post doctoral research associate in the Computer Science Department of Purdue University. She conducts research on security for distributed systems, with particular focus on trust management, identity management and access control for grids and Web Services. She has published several refereed journal and conference papers in these areas. She has been the main architect of the Trust-X system, an innovative system supporting trust negotiation in distributed open systems.