The aim of the present book will be to provide a comprehensive account of our present knowledge of the theory of dynamical phenomena exhibited by elose binary systems; and on the basis of such phenomena as have been attested by available observations to outline probable evolutionary trends of such systems in the course of time. The evolution of the stars - motivated by nuelear as weIl as gravitation al energy sources - constitutes nowadays a well- established branch of stellar astronomy. No theo­ ries of such an evolution are as yet sufficently specific - let alone infallible - not to require continual tests by a confrontation