The Russian edition of this book appeared in 1969 and im- mediately gained widespread recognition as a reference work for research workers interested in the physiology, biophysics, and pharmacology of excitable tissues. There are several reasons for the book's success. It deals with a key problem in biology which has recently been the subject of very intensive study and it is of great interest to a wide scientific audience. Not only the fundamentals of the modern membrane theory of biopotentials, but also the vast factual material collected in the last decades by the study of the biophysical and pharmacological properties of the ionic permeability pores of the cell membrane, are described in the book in an authoritative yet readable form. Special attention is paid in the book to the systematic analysis of the consequences of the Hodgkin-Huxley mathematical theory of the nervous impulse for the problem of excitability. The relationship between the various parameters of excitability (threshold potential, threshold current, useful time), accommodation, and the action potential on the one hand, and the constants of ionic permeability of the nerve fiber membrane, on the other hand, is subjected to detailed examination in this context. To do this, the author has made extensive use not only of experimental results obtained on isolated fibers (especially single nodes of Ran- vier), but also the results of his own investigations on mathematical models of excitable membranes.