In the period between the birth of quantum mechanics in the 1920s and the late 1960s, V.A. Fock wrote papers that are now deemed classics in the field. This collection explores such fundamental notions of theoretical quantum physics as the Hartree-Fock method, Fock space, Fock symmetry of the hydrogen atom, and the Fock functional method. Fock was a key contributor to one of the most exciting periods of development in 20th-century physics, and this book conveys the essence of that time. These seminal works are a helpful reference for any undergraduate, graduate, or researcher in theoretical and mathematical physics, especially those specializing in quantum mechanics and quantum field theory.