Microbes are microscopic; thus, we cannot see them by the naked eye. Antoni van Leeuwenhoek crafted the first microscope lenses that magnified over 200 times, and he turned his lenses towards everything. He saw blood cells, sperm, hatching ants, and every cellular microbe groups that we know of today. About 150 years later, Louis Pasteur’s meticulously designed swan-necked flask experiments were instrumental in putting off the spontaneous generation hypothesis for microbes. Pasteur showed that microbes arise from microbes, and they are not generated spontaneously from non-living matter. Before any microbe has ever been linked to a disease, the independent death rate analyses of Semmelweis and Nightingale led to the introduction of procedures that we call antiseptic today. Koch was the first to photograph a pathogen in infected tissue; he also laid down guidelines on how to link a microorganism to a disease. These guidelines are Koch’s postulates. Only a few microbes cause disease; most microbes are harmless. Microbes are present in all three domains of life: Bacteria, Archaea, and Eukaryota.