The purpose of this course is to provide a conceptual framework for understanding the behavior of engineering (solid) materials by emphasizing important relationships between internal structure and properties. It attempts to present a general picture of the nature of materials and the mechanisms that act upon, modify, and control their properties. The subject matter is meant to provide prospective scientists with sufficient background and understanding to appreciate existing materials and to exploit new materials development effectively in energy-related research and engineering. This course has three main parts. The first part treats the internal structure of materials, both perfect and imperfect. The second part deals with basic concept of equilibrium in solids (phase diagram) as well as kinetic problems of diffusion, phase transformations, and structure control. The third part covers the mechanical and electrical properties of solid materials showing the relation to structure.