An overview of the optical effects in solids, addressing the physics of various materials and their response to electromagnetic radiation. The discussion includes metals, semiconductors, superconductors, and insulators. The book begins by introducing the dielectric function into Maxwell's macroscopic equations and finding their plane-wave solution. The physics governing the dielectric function of various materials is then covered, both classically and using basic quantum mechanics. Advanced topics covered include interacting electrons, the anomalous skin effect, anisotropy, magneto-optics, and inhomogeneous materials. Each subject begins with a connection to the basic physics of the particular solid, after which the measurable optical quantities are derived. It allows the reader to connect measurements (reflectance, optical conductivity and dielectric function) with the underlying physics of solids. Methods of analysing experimental data are addressed, making this an ideal resource for students and researchers interested in solid state physics, optics, and materials science.