In the early 1680s, a Dutch linen-merchant named Antoni van Leeuwenhoek published his findings on bacteria, including the first drawings of them. His observations — made possible with lenses of his own making — were wide-ranging and highly accurate for the time. He found inhabitants of his newly discovered universe in a variety of places, including rainwater and tooth scrapings, and called these small organisms "animalcules."

Microbiology can be said to have begun with these singular findings and those of Robert Hooke and others. Though microscopes predate Leeuwenhoek, he was the first to produce lenses capable of an almost 300-fold magnification — permitting him to cross the visual threshold into the microbial universe. Current imaging technology allows magnification of 25 million times or more, revealing the microbial world in greater detail. With the current generation of advanced imaging techniques, for example, scientists are able to image the surface structure of the protein coats of viruses down virtually to the level of individual atoms.