Included in the present volume are selected pages from Volume I, II, and IV of the CRC Handbook of Microbiology. Data from Volume II has not been included (microbial products), which did not lend itself readily to the selection of a few pages. As it is the present volume includes information about the various groups of microorganisms, their cell walls, and their genetics. Data on amino acids, carbohydrates, and lipids re included, together with diagrams of metabolic pathways and information on immunocompetent cells. General reference data include a glossary, statistical tables and other information that is hoped to be found useful by the reader.