This document provides an introduction to microbiology. It defines microbiology as the study of microorganisms like bacteria, fungi, algae, protozoa and viruses. These microorganisms are too small to be seen with the naked eye and are present everywhere in the environment and in and on humans and other animals. Microorganisms can be beneficial or harmful. The document then outlines the main branches of microbiology like bacteriology, mycology, and parasitology. It also discusses several applied branches like medical microbiology, pharmaceutical microbiology, and food microbiology. Finally, it reviews some important figures in the history of microbiology like Louis Pasteur, Robert Koch, Joseph Lister and their contributions to the field