A text for second-year graduate students who are presumably familiar with basic differential, integral, and vector calculuses, and partial differentiation at the sophomore-junior level. The first seven chapters review the free-electron model of a metal, theory of lattice vibrations, theory of Bose-Einstein condensation, Bloch electrons and second quantization formalism. Later chapters treat the microscopic theory of superconductivity, including all basic thermodynamic properties of type I superconductors; quasi-particles, quasi- electrons, and pairons; and type II compounds.