Volume 3 of “Methods in Microbiology” is concerned with the techniques used for isolating, growing and preserving micro-organisms. We considered that information on these themes was required in two distinct forms: a comprehensive list of growth media which would provide the reader with easy access to formulae and growth conditions for a wide range of micro-organisms, and detailed descriptions of the special methods used for certain selected groups of micro-organisms. In addition general articles describing the principles involved in enrichment techniques for different types of micro-organisms and for the isolation of mutants and the design of mutation/selection programmes are also relevant to the main theme. As the contributions to Volume 3 took shape it became apparent that the amount of material involved was too much for inclusion in one volume and the material split relatively easily into two sub-volumes which are called Volumes ЗА and 3B. Volume ЗА contains Chapters concerned with the composition of growth media and media tables. Tabulated information about the preservation of micro-organisms and general articles concerned with enrichment, mutation and strain selection procedures are also provided. Volume 3B deals entirely with selected groups of micro-organisms, the emphasis being on methods of isolation, growth and handling in the laboratory, and preservation of cultures. In selecting the particular groups described we have been concerned to choose organisms which are not well described in other publications or which involve, because of their unusual physiology, special techniques. The actual treatment of the material we have left very largely to the choice of the individual authors. Our aim throughout has been to provide a useful treatment of important topics which are not well covered elsewhere while at the same time avoiding pointless repetition of readily available information.