In the field of aeronautics, trajectory planning and control have always been important research areas. Trajectory planning, unlike path planning, involves assigning time information to the path. Fixed-wing Unmanned Aerial Vehicles (UAVs) must follow specific trajectories during flight to accomplish tasks such as cruising, landing, and obstacle avoidance. Differential flatness control is considered a suitable method for low-level control of fixed-wing UAVs, as it enables efficient control of predetermined trajectories. This chapter examines the topic of trajectory planning and differential flatness control for fixed-wing UAVs. First, the coordinated flight model for fixed-wing aircraft is introduced. Next, the principles of trajectory tracking using the coordinated flight model and differential flatness control are explored.