This book presents a fair and balanced description of dynamics problems and formulations. From the classical methods to the newer techniques used in today's complex and multibody environments, this text shows how those approaches complement each other. The text begins by introducing the reader to the basic concepts in mechanics. These concepts are introduced at the particle mechanics level. The text then extends these concepts to systems of particles, rigid bodies (plane motion and 3D), and lightly flexible bodies. The cornerstone variational principles of mechanics are developed and they are applied to particles, rigid bodies, and deformable bodies. The text emphasizes both the derivation of the describing equations and the response. The describing equations are developed using force and moment balances, as well as variational principles. Different approaches of obtaining equations of motion are discussed and compared. The response is analyzed qualitatively and quantitatively.