Microbiology is the study of organisms that are too small to be seen with the unaided eye: Bacteria, Archaea, viruses, and unicellular eukaryotes.

To study microbiology is to pursue the breadth of biology, as microorganisms provide experimental material for understanding physiology; cell structure and function; biochemistry; molecular biology; photosynthesis; ecology; evolution; genetics; development; and even simple behavioral responses and "memory." Studies with microorganisms continue to lay the foundation for molecular genetics, recombinant DNA research, biotechnology, environmental sciences, and many areas of biochemistry.