Microbiology (from Greek lang: μῑκρος, mīkros, "small"; lang: βίος, bios, "life"; and lang: -λογία, -logia) is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. This includes eukaryotes such as fungi and protists, and prokaryotes, which are bacteria and archaea. Viruses, though not strictly classed as living organisms, are also studied. In short; microbiology refers to the study of life and organisms that are too small to be seen with the naked eye.

Microbiology is a broad term which includes virology, mycology, parasitology, bacteriology and other branches. A microbiologist is a specialist in microbiology.

Microbiology is researched actively, and the field is advancing continually. We have probably only studied about one percent of all of the microbe species on Earth. Although microbes were first observed over three hundred years ago, the field of microbiology can be said to be in its infancy relative to older biological disciplines such as zoology and botany.

Pre-microbiology

The existence of microorganisms was hypothesized for many centuries before their actual discovery in the 17th century. The first theories on microorganisms was made by Roman scholar Marcus Terentius Varro in a book titled On Agriculture in which he warns against locating a homestead in the vicinity of swamps: cquote: ...and because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases. This passage seems to indicate that the ancients were aware of the possibility that diseases could be spread by yet unseen organisms.

In The Canon of Medicine (1020), Abū Alī ibn Sīnā (Avicenna) stated that bodily secretion is contaminated by foul foreign earthly bodies before being infected.Ibrahim B. Syed, Ph.D. (2002). "Islamic Medicine: 1000 years ahead of its times", Journal of the Islamic Medical Association 2, p. 2-9. He also hypothesized on the contagious nature of tuberculosis and other infectious diseases, and used quarantine as a means of limiting the spread of contagious diseases.

When the Black Death bubonic plague reached al-Andalus in the 14th century, Ibn Khatima hypothesized that infectious diseases are caused by "minute bodies" which enter the human body and cause disease.Ibrahim B. Syed, Ph.D. (2002). "Islamic Medicine: 1000 years ahead of its times", Journal of the Islamic Medical Association 2, p. 2-9.