The growing popularity of Service Oriented Architectures is mainly due to business and technology trendsthat have crystallized over thepast decade. On the business side companies struggle to survive in a competitive - vironment that pushes them towards a tighter integration into an industry s value chain to outsource non core business operations or to constantly- engineer business processes. These challenges boosted the demand for sc- able IT-solutions with e?orts ultimately resulting in a ?exible architectural paradigm - Service Oriented Architectures. On the technical side middleware standards technologies and archit- turesbasedonXMLand Webservicesaswellastheirsecurityextensionshave matured to a sound technology base that guarantees interoperability across enterprise and application boundaries - a prerequisite to inter-organizational applications and work?ows. While the principles and concepts of Service Oriented Architectures may lookevidentandcogentfromaconceptualperspective therealizationofint- organizational work?ows and applications based on the paradigm Service Oriented Architecture remains a complex task and all the more when it comes to security the implementation is still bound to low-level technical knowledgeandhence error-prone. The number of books and publications o?ering implementation-level c- erageofthetechnologies standardsandspeci?cationsasrequiredbytechnical developers lookingfor guidance on how to add security to service oriented solutions based on Web services and XML technology is already considerable and ever growing. The present book sets a di?erent focus. Based on the p- adigmof Model Driven Security it shows how to systematically designand realize security-critical applications for Service Oriented Architectures.