This is an introductory book on helicopter dynamics. The aim of this book is to introduce the students/engineers to the basic principles of helicopter dynamics. The book focuses on three major topics: (i) rotor blade idealization and blade dynamics in flap, lag, and torsion modes, (ii) rotor blade aeroelastic stability (coupled flap-lag and coupled flap-torsion), (iii) coupled rotor-fuselage dynamics. It covers hover, forward flight, and other maneuver flights. Starting from basic physics of rotating systems, the equations of motion have been derived in vector form.