The electron theory of solids has attracted great attention in recent years, mainly because of the numerous practical applications of semicon­ ductors. However, all the reviews and monographs on this subject deal only with crystalline conductors. At present, mainly in the Soviet Union, experimental and theoretical investigations have been extended to liquid and solid amorphous conductors, and in particular to such semiconductors. However, all the work published so far in this field is in the form of separate papers scat­ tered throughout various journals, and there has as yet been no Soviet or for­ eign review of the theoretical work on amorphous semiconductors, in spite of the increasing interest in them. The investigation of liquid and amorphous semiconductors is of great practical importance, first, because all the solid semico'nductors are usually prepared from the liquid phase and it is important to know the electrical and other properties of this phase; secondly, amorphous semiconductors are beginning to be used in industry, for example, amorphous Sb S films in vidicon tubes. In some cases, especially in optical instruments, 2 S amorphous semiconductors have advantages compared with crystals. Theore­ tical studies of amorphous semiconductors should help in these practical applications. The present monograph is the first attempt to present systematically the quantum electron theory of amorphous conductors. The most interesting-in the author's view-theoretical papers on this subject, published in journals are reviewed and critically compared.