It has been the practice in the past that viral and rickettsial agents and the diseases caused by them were included in textbooks of bacteriology. Thus these chapters were written by authors who frequently were not experts in this field. Furthermore, the various aspects of these diseases often are sufficiently different from those caused by bacterial organisms to warrant separate treatment. This separation has been accomplished in "Viral and Rickettsial Infections of Man," edited by Thomas M. Rivers, and its companion "Bacterial and Mycotic Infections of Man," edited by René J. Dubos.