The possible existence of unseen microbial life was suspected from ancient beef intestine, such as in Jain scriptures from sixth century BC India. The scientific study of microorganisms began with their observation under the microscope in the 1670s by Anton van Leeuwenhoek.

Because microorganisms include most unicellular organisms from all three domains of life they can be extremely diverse. Two of the three domains, Archaea and Bacteria, only contain microorganisms. Antonie van Leeuwenhoek was the first to study microscopic organisms. Lazzaro Spallanzani showed that boiling a broth stopped it from decaying.

Vardhmana Mahavira postulated the existence of microscopic creatures in the sixth century BC. The possible existence of microscopic organisms was discussed for many centuries before their discovery in the seventeenth century. By the sixth century BC, the Jains of present-day India postulated the existence of tiny organisms called nigodas. The earliest mention of micro organisms is found in hindu scriptures like the Atharvaveda, compiled 1200 BCE-1000 BCE, where Rishi Kanva refers to the microbes as Kirmis. He, along with his descendants Yamadagnni and Agasti, composed mantra suktas which highlight microbial infections and possible ways to cure them.

Rishi Agastya composed a mantra in Rig Veda which refers to two types of harmful creatures for ones body. The first being visible and second being so minuscule that they are invisible to the naked eyes. The Shanti Parva of Ved Vyas Mahabharata mentions organisms that are so minuscule that they can’t be seen with naked eyes but only inferred. There are many creatures that are so minute that their existence can only be inferred. With the failing of the eyelids alone, they are destroyed. Avicenna suggested that tuberculosis and other diseases might be contagious. It is incorrect to assume that diseases appear one by one in humans.