This book is dedicated to the Soviet theoretician Yakov Ilich Frenkel (1894 - 1952), whose work in solid and liquid state physics is considered to be the golden foundation of twentieth century physics. Best known are the Frenkel pairs (defects), kinetic theory of liquids, theory of mobile dislocations (Frenkel- Kontorova solitons). Today, the electron theory of solids is inconceivable without excitons - the quasiparticles he introduced in 1930. Frenkel also contributed important concepts to classical electrodynamics (which now go under Feynmana ~s appellation "Frenkela ~s Fields") and to...