An Introduction to the Electron Theory of Solids introduces the reader to the electron theory of solids. Topics covered range from the breakdown of classical theory to atomic spectra and the old quantum theory, as well as the uncertainty principle of Heisenberg and the foundations of quantum mechanics. Some problems in wave mechanics and a wave-mechanical treatment of the simple harmonic oscillator and the hydrogen atom are also presented. Comprised of 12 chapters, this book begins with an introduction to Isaac Newton's theory of classical mechanics and how the scientists after him discounted his ideas. The discussion then turns to the spectrum of atomic hydrogen and the old quantum theory; Heisenberg's uncertainty principle and the consequences of wave-particle duality; the foundations of quantum mechanics; and assemblies of atoms. Atoms in motion and statistical mechanics are also considered, along with simple models of metals and the band theory of solids. The final chapter presents some results of band theory, with particular reference to thermal ionization of impurity atoms and conductivity of metals. This monograph is primarily intended for students of any discipline.