By identifying unifying concepts across solid state physics, this text covers theory in an accessible way to provide graduate students with an intuitive understanding of effects and the basis for making quantitative calculations. Each chapter focuses on a different set of theoretical tools, using examples from specific systems and demonstrating practical applications to real experimental topics. Advanced theoretical methods including group theory, many-body theory, and phase transitions are introduced in an accessible way, and the quasiparticle concept is developed early, with discussion of the properties and interactions of electrons and holes, excitons, phonons, photons, and polaritons. New to this edition are sections on graphene, surface states, photoemission spectroscopy, 2D spectroscopy, transistor device physics, thermoelectricity, metamaterials, spintronics, exciton-polaritons, and flux quantization in superconductors. Exercises are provided to help put knowledge into practice, with a solutions manual for instructors available online, while appendices review the basic mathematical methods used in the book.