This book has evolved out of roughly ve years of working on computing with social trust. In the beginning, getting people to accept that social networks and the relationships in them could be the basis for interesting, relevant, and exciting c- puter science was a struggle. Today, social networking and social computing have become hot topics, and those of us doing research in this space are nally nding a wealth of opportunities to share our work and to collaborate with others. This book is a collection of chapters that cover all the major areas of research in this space. I hope it will serve as a guide to students and researchers who want a strong introduction to work in the eld, and as encouragement and direction for those who are considering bringing their own techniques to bear on some of these problems. It has been an honor and privilege to work with these authors for whom I have so much respect and admiration. Thanks to all of them for their outstanding work, which speaks for itself, and for patiently enduringall my emails. Thanks, as always, to Jim Hendler for his constant support. Cai Ziegler has been particularly helpful, both as a collaborator, and in the early stages of development for this book. My appreciation also goes to Beverley Ford, Rebecca Mowat and everyone at Springer who helped with publication of this work.