The theory of relativity was created in 1905 to solve a problem concerning electromagnetic fields. That solution was reached by means of profound changes in fundamental concepts and ideas that considerably affected the whole of physics. Moreover, when Einstein took gravitation into account, he was forced to develop radical changes also in our space-time concepts (1916). Relativistic works on heat, thermodynamics, and elasticity appeared as early as 1911. However, general theories having a thermodynamic basis, including heat conduction and constitutive equations, did not appear in general relativity until about 1955 for fluids and appeared only after 1960 for elastic or more general finitely deformed materials. These theories dealt with materials with memory, and in this connection some relativistic versions of the principle of material indifference were considered. Even more recently, relativistic theories incorporating finite deformations for polarizable and magnetizable materials and those in which couple stresses are considered have been formulated. A broader description of the development of these relativistic topics is contained in § 13. The purpose of this book is to describe the foundations of the general relativistic theories that include constitutive equations, and to present some applications, mainly to elastic waves, of these theories. This tract is divided into two parts. In the first part only the Eulerian point of view is considered; basic equations of general relativity, other than constitutive equations, are stated in full generality (except for couple stresses which are considered in part 2). Part 1 also thoroughly covers fluids, including constitutive equations.