The most valuable service Dr. Gel'man and her colleagues have performed for the many investigators of bacterial membrane systems in producing their first excellent monograph on "The Respiratory Apparatus of Bacteria" in 1966 has been continued and expanded in the preparation of this volume. The au­ thors have brought together in a single volume much of the detail of investiga­ tions of bacterial membranes at the ultrastructura11eve1 and the chemical and biochemical organizationa11eve1s. The approach in bringing together this rap­ idly increasing volume of discovery has been both comprehensive and system­ atic, with a constant awareness of the importance of the molecular and func­ tional properties and relationships existing in various bacterial membranes. The monograph naturally reflects the authors' interest and their own inti­ mate involvement in the elucidation at the molecular level of the respiratory chains organized in the prokaryotic bacterial membrane system. It is entirely appropriate that the chapter devoted to this topic should occupy a substantial proportion of this monograph. Indeed, had this volume been prepared at this very moment, that proportion would have been even greater, as the work in .