This book studies the key techniques of polar codes in the application of the state-of-art UAV-enabled (relaying) communication systems from the theoretical and practical points of view. The aim of this book is thus to shed some light on the challenges and difficulties of polar coding for (aerial) relay transmission systems from five aspects, i.e., achievability of system capacity, implementation/algorithm complexity, cooperative transmission protocol design, practical application performance, and security. This book can provide key algorithm and simulation result supports for the application of (secure) polar codes in the next generation wireless communication systems integrated with UAVs.