Now available in a convenient paperback edition! Volume 1 treats in detail the fundamental concepts of the theory of groups and their role in physics, plus their application to molecular and solid state physics. In Volume 2 the theory of Lie groups and Lie algebras is presented and applied to atomic and high-energy physics, concluding with an account of the recently developed gauge theories of fundamental interactions. The extensive appendices contain background material and comprehensive tabulations of ther properties of crystallographic point groups and semi-simple Lie groups and Lie algebras.