This chapter charts how the 1964 discovery of tetrahydrocannabinol and cannabidiol led to the 1988 discovery of the Endocannabinoid System (ECS), the largest receptor system and the master regulator of homeostasis in the human body and discusses how and why cannabinoids interact with CB1 and CB2 receptors to treat a vast number of illnesses. The ECS maintains the body’s homeostasis, acting as a chemical bridge between body and mind. It regulates blood sugar, immune function, muscle and fat tissues, hormones, pain centers, reward centers, and metabolic functions. Cannabis’ Schedule I status is the reason that no research institution has ever administered anandamide to a human being.