Surveys the contemporary concepts and theoretical and experimental results of tunneling processes. Examines from a unified viewpoint not only chemical reactions but also other physical physicochemical and biological phenomena in which the tunneling effect is of great importance. Covers the general ideas of tunneling, the low temperature chemical reactions that manifest tunneling mechanisms, tunneling effects in amorphous materials, quantum diffusion and surface phenomena in quantum crystals, hopping diffusion and tunneling scavenging of electrons, and tunneling effects in biological systems.