With the emergence of services for professional and private on-line collaboration via the Internet, many European citizens spend work and leisure time in on-line communities. Users consciously leave private information; they may also leave personalized traces they are unaware of. PICOS will develop and build a state-of-the-art platform for providing the trust, privacy and identity management aspects of community services and applications on the Internet and in mobile communication networks. The PICOS approach to trustworthy on-line community collaboration addresses these four questions: What are the Trust, Privacy and Identity issues in new context-rich mobile communication services, especially community-supporting services? How can information flows and privacy requirements be balanced in complex distributed service architectures (e.g., mash-ups)? How can these issues be solved in an acceptable, trustworthy, open, scalable, manner? Which supporting services and infrastructures do the stakeholders need?The PICOS consortium includes European industry and research communities. The project will first review contemporary research in relevant disciplines. Its platform design and prototype development work will then create interoperable, open, privacy-respecting identity and trust management tools that can be demonstrated to the public. These will be used to construct community application prototypes by leading industry partners; those will be trialled with selected on-line communities. PICOS will self-evaluate usability, ergonomics, legal issues, trust and privacy. Expected PICOS results are:•A set of interdisciplinary requirements for trustworthy, privacy-friendly community transactions,•A platform prototype that demonstrates the provision of state-of-the-art privacy and trust technology to community applications,•User-centric trials that validate its applicability,Publications and a final report will disseminate the PICOS results to the public.