Self-organized networks based on mobile devices, e.g., mobile ad hoc networks (MANET), are becoming a practical platform for mobile social networking. People, either familiar or strangers, communicate with each other via such a network for instant social activities. How to help mobile users to build up trust in mobile social networking is becoming an important and interesting issue. Trust concerns not only security, but also privacy, as well as quality of social networking experiences. It relates to many properties that are essential for establishing a trust relationship in ephemeral and dynamically changed mobile social environments. This book chapter reviews the literature with regard to how to build up trust in mobile social networking. We explore whether mobile social networking is demanded, considering many existing popular Internet social networking services. Based on a need assessment survey, we propose a trust management framework that supports context-aware trust/reputation generation, trustworthy content recommendations, secure communications, unwanted traffic control, user privacy recommendation and preservation, and other trust and privacy enhancement technologies. Simulations, prototype implementation, and trial experiments further prove the effectiveness of proposed solutions.