This book is devoted to the basic variational principles of mechanics, namely the Lagrange-D'Alembert differential variational principle and the Hamilton integral variational principle. These two variational principles form the basis of contemporary analytical mechanics, and from them the body of classical dynamics can be deductively derived as a part of physical theory. In recent years variational techniques have evolved as powerful tools for the study of linear and nonlinear problems in conservative and nonconservative dynamical systems, as is emphasized in this book.