Cordyceps is one of the most valued medicinal fungi in all of Classical Chinese Medicine. Once reserved exclusively for emperors, this versatile mushroom is now the tonic of choice among world-class competitive athletes. Cordyceps attracted public attention when a group of Chinese runners, who reported using Cordyceps extract to enhance endurance and recovery, broke nine world records in the World Outdoor Track and Field Championships in Germany. Modern clinical applications and research closely mirror those uses described in Classical Chinese Medicine. Clinically, Cordyceps is used to build and support immune function in various immune compromised conditions including chronic fatigue, cancer, and respiratory conditions, especially asthma.