The physical nature of engineering materials can be described by a set of measurable properties. This chapter defines these measures and discusses their implications in a broad sense. It also covers Material Science, i.e. the science of producing materials with intended properties, and outlines different types of engineering materials and their characteristic qualities. Later in the book, some of these matters will be further investigated by the powerful theories of Continuum Mechanics, FEM etc., which will bring a much more potent and general understanding of solid materials.