Synopsis The second edition retains the basic organisation and scope of the earlier edition. However, notable additions have been made in the chapters on structure, genetics and evolution. A short description of groups like cyanobacteria and archaebacteria has also been added. An outline of the bacterial classification as given in the recent four-volume edition of Bergey's manual is given for ready reference. A chapter on genetic engineering bas been provided to keep up with the advances in the understanding of the microbial world. The list of nobel prize winners has been revised and the major events in commercialisation of biotechnology have been listed. There was a strong pressure to enlarge the chapter on bacterial diseases. But it was decided to write another volume which should include all the aspects of bacterial diseases of plants. As always, all comments and criticism from readers are most welcome. It is hoped that this revised volume would attract the imagination of students so that the subject becomes more popular.