Rapid increase in information in medical sciences requires that textbooks be revised and updated to keep pace with the current trends. The seventh edition of the book is an updated version and elegantly meets the new course requirements of undergraduate medical students. The text has been thoroughly revised as per the Competency Based Undergraduate Curriculum for the Indian Medical Graduate. However, for the ease of learning and teaching traditional organism-based subject, brief description has been retained. Description of clinical case-based exercises, monkey pox and SARS-CoV-2 virus has been added.This edition also features incorporation of parasitology, which has been deftly included to add value to the book. Unnecessary details of various parasites have been excluded. This obviates the reading of a separate book on parasitology.The text is presented in a simple and lucid manner. It is fully illustrated with colour and computer-drawn diagrams, clinical photographs and photomicrographs. These make the book attractively colourful and the readers can have a far better understanding of the biology of microorganisms. New illustrations have been added at various places for in-depth comprehension of the topics.For quick review and recapitulation, key facts and multiple choice questions have been added at the end of each chapter. To help the students perform better in the examination, the competencies expected from the students after reading various chapters have been outlined in the beginning of the chapters.