This document provides an introduction to microbiology. It defines microbiology as the study of microorganisms that are too small to be seen with the naked eye, including bacteria, archaea, viruses, fungi and protozoa. These microbes play key roles in processes like nutrient cycling, biodegradation, and food spoilage. Microorganisms are found everywhere, including in humans, animals, plants, soil, water and air. They have both beneficial and detrimental impacts on human life, and are used to produce important products like antibiotics, enzymes and vitamins. The field of microbiology has wide applications in areas such as medicine, industry, agriculture, and food science.