Nearly twenty years ago a symposium convened at Dallas, Texas, to con sider the place of atypical mycobacteria among agents of human disease. An edited and condensed version of that symposium was subsequently published and since that time has constituted the only bound source of infor mation covering broad aspects of mycobacterial disease. In the years since a vast amount of information has accumulated in periodical literature, some of which is not readily accessible. The time seems suitable for a comprehensive collection of this scattered material into a single book. The aim has not been to produce an exhaustive account of mycobacteria and mycobacterioses, but rather to concentrate on salient points and particularly on those most generally useful to a diverse group of interests: mycobacteriology, pathology, epidemiology, and, of course, clinical fields. In Appendix A there appear in summary form manifestations of myco bacteria as they have occurred among clinical specialities, such as ortho pedic surgery, dermatology, and urology. These summaries are designed to serve as guides to more probable infections and to lead to more extensive reading with respect to the specific organism encountered. Appendix C presents, also in summary form, drugs, regimens, duration of treatment, and toxicities to permit ready reference to less familiar anti microbial agents. These are suggestive only, useful when the general nature of the organism is known but not the specific susceptibility of the individual strain.