The cannabis plant contains over 100 cannabinoids along with other substances. The effects of these compounds on the human body are not fully known. Ongoing research is helping us better understand the pharmacokinetic, pharmacodynamic, and physiological effects of these compounds and recognize the medical benefits. As we begin to comprehend the effects of these substances, a good understanding of the pharmacology is important. This chapter reviews the pharmacology of cannabis, beginning with an overview of the cannabis plant followed by a review of the endocannabinoid system. It goes into more detail with the two main cannabinoids, namely Δ9-Tetrahydrocannabinol (THC) and Cannabidiol (CBD), providing details on the pharmacokinetics and metabolism of these compounds. Finally, the chapter reviews the different routes of administration that cannabis is being used as well as insight to interactions with other medications.