Mobile opportunistic networks are formed by mobile users who share similar interests and connect with one another by exploiting Bluetooth and/or WiFi connections. Such networks not only re-assemble the real-world interaction between people, but also can effectively propagate data among mobile users. This book focuses on QoS-aware data query and transmission in mobile opportunistic networks. This book consists of six chapters. Chapter 1 provides an introduction to the mobile opportunistic networks. Chapter 2 discusses the background, related work and motivation of this book. Chapter 3 presents efficient data query in mobile opportunistic networks. Chapter 4 introduces efficient quality-of-service (QoS) support in mobile opportunistic networks. Delay-constrained least-cost multicasting in mobile opportunistic networks is discussed in Chapter 5. Finally, Chapter 6 concludes the book.