This is the Proceedings of the Taniguchi International Symposium on "Relaxation of Elementary Excitations" which was held October 12-16,1979, at Susono-shi (at the foot of f1t. Fuji) in Japan. The pleasant atmosphere of the Symposium is evidenced in the picture of the participants shown on the next page. The purpose of the symposium was to provide an opportunity for a limited number of active researchers to meet and to discuss relaxation processes and related phenomena not only of excitons and phonons in solids but also electronic and vibrational excitations in molecules and biological...