This book documents the R&D outcome of the PRIME Project, an R&D project partially funded by the European Union Sixth Framework Programme and the Swiss Federal Office for Education and Science.  PRIME has focused on privacy-enhancing identity management techniques and systems to support users’ sovereignty over their personal privacy and enterprises’ privacy-compliant data processing. During the course of four years, the project has involved over a hundred researchers and professionals from 22 major European academic and industrial organizations conducting R&D work in areas relevant to digital privacy. The book presents 28 detailed chapters organized in five parts: Introductory summary, legal, social, and economic aspects, realization of privacy-enhancing user-centric identity management, exploitation of PRIME results for applications, conclusions drawn and an outlook on future work. As the first coherent presentation of the topic, this book will serve as a valuable source of reference and inspiration for anybody working on digital privacy.