This book presents the non-linear theories of continuum thermomechanics. The author emphasizes issues that are foundational in nature and seeks results common to materials of arbitrary symmetry. The central part deals with thermoelastic bodies with heat conduction and viscosity, including the inviscid or ideal dissipationless bodies. A surprising variety of phenomena can be modeled within this framework. The main ideas can be transferred into more complicated theories of materials with memory or microstructure. A large portion is an extension of Gibbs' ideas to bodies of general symmetry by the methods of the calculus of variations. The interplay between the convexity properties of the stored energy functions, the resulting equations, and the physics is also discussed.