This book presents the most interesting talks given at ISSE 2009 - the forum for the inter-disciplinary discussion of how to adequately secure electronic business processes. The topics include: - Economics of Security and Identity Management - Security Services and Large Scale Public Applications - Privacy and Data Protection and Awareness Raising - Standards and Technical Solutions - Secure Software, Trust and Assurance Adequate information security is one of the basic requirements of all electronic business processes. It is crucial for effective solutions that the possibilities offered by security technology can be integrated with the commercial requirements of the applications. The reader may expect state-of-the-art: best papers of the Conference ISSE 2009.