The chapter offers a brief review and features multiple-choice questions on microbiology. Microbiology is a science that deals with the study of living organisms that cannot be seen by the naked eye. These can be seen with the aid of microscopes, which magnify objects. The topics that are briefly covered in this chapter include history of microbiology, stains and staining reactions, sterilization, pure culture methods, medical microbiology microbial diseases, respiratory tract infections, urinary tract infections, sexually transmitted diseases, bacterial infections of gastrointestinal tract, types of clinical manifestations, structure and development of immune system. Sterilization is the freeing of an article from all living organisms, including bacteria and their spores.