Cordyceps militaris is the type species of the genus Cordyceps which includes about 400 described species. It is a well known entomopathogen that infects moth pupae throughout much of the Northern Hemisphere. It multiplies in the host and after overwintering the fungus ruptures the host body forming a yellowish-orange club like stroma carrying several perithecia. The stroma is traditionally used as a therapeutic agent in oriental countries and scientific studies has identified the presence of metabolites with health-stimulating properties. Medicinal fungi like C. militaris has been used in Eastern countries including China over hundred years and is now becoming promising, complementary and alternative medicines in western countries. The cordycepin, 3'-deoxyadenosine, produced by this fungus has antifungal activities and has been tested for potential use against cancer.