The book is written following the syllabus framed by Veterinary Council of India (VCI). It comprises historical introduction, morphology, classification, resistance, natural habitat, genome, isolation and colony characteristics, biochemical and antigenic properties, pathogenesis, disease produced and diagnosis of each bacterial genus associated with animal and human health. The book is intended to help BVSc and Post Graduate students of Veterinary Microbiology as well as the aspirants of ICAR-JRF, ICAR-NET/ARS examinations. Further, it will also help the person engaged as Veterinarian or in the laboratory for the diagnosis of animal diseases. As the book comprises the diagnostic technique for each bacterial genus ranging from staining parameters to molecular tools.