This book focuses on the trajectory design technologies of unmanned aerial vehicles (UAVs) in wireless networks. Multiple pure trajectory design and joint design schemes have been proposed, from the trajectory characterization and optimization to simulation evaluations. Different UAV-Aided wireless communication networks have been considered, involving wireless power transfer (WPT), integrated sensing and communications (ISAC), data collection and covert communication. An in-depth study on privacy-preserving for UAV has also been presented. The book benefits researchers, engineers, and graduate students interested in the wireless communication system, UAV-assisted networks.