This book discusses the dynamics of a tail-sitter quadrotor and biplane quadrotor-type hybrid unmanned aerial vehicles (UAVs) and, based on it, various nonlinear controllers design like backstepping control (BSC), ITSMC (Integral Terminal Sliding Mode Control), and hybrid controller (BSC + ITSMC). It discusses single and multiple observer-based control strategies to handle external disturbances like wind gusts and estimate states. It covers the dynamics of slung load with a biplane quadrotor and a control architecture to handle the effect of partial rotor failure with wind gusts acting on it. An anti-swing control to prevent damage to the slung load and a deflecting surface-based total rotor failure compensation strategy to prevent damage to the biplane quadrotor are also discussed in this book. The monograph will be helpful for undergraduate and post-graduate students as well as researchers in their advanced studies.