Book excerpt: Essentials of Microbiology is an extensive guide to all aspects of microbiology covering immunology, bacteriology, virology, medical mycology, diagnostic medical microbiology, and many miscellaneous infections. Microbiologist have made significant contributions to basic biological sciences as well as in the applied areas of public health and medical sciences, agriculture, industry and environmental sciences. The most dramatic current development in applied microbiology is due to development of genetic engineering and recombinant DNA technology. Life is governed by a relatively small number of molecular reactions that exploit a limited variety of simple concepts. However, their combination has led to an amazing chemical diversity which is still beyond the reach of the microbiologists even in the most complex supra-molecular systems, despite a huge set of synthetic methods. Microbiology is the study of microorganisms, which are microscopic, unicellular, and cell-cluster organisms. This includes eukaryotes such as fungi and protests, and prokaryotes. Viruses and prions, though not strictly classed as living organisms, are also studied. Microbiology typically includes the study of the immune system, or Immunology. This book will be useful to researchers, teachers and students of microbiology, botany, zoology and agriculture.