Microbiology is the study of extremely small organisms. This includes organisms like bacteria, fungi, protozoa, and viruses.
- Brock's Biology of Microorganisms: A comprehensive undergraduate level textbook.
- The Physiology and Biochemistry of Prokaryotes: A thorough graduate-level textbook on the physiology and metabolism of bacteria and archaea. Does not include eukaryotes like fungi or protozoa.
- Todar's Online Textbook of Bacteriology: a free online textbook on introductory microbiology, emphasizing bacteria.