In this Handbook, philosophers from around the world address the metaphysics, epistemology, and value of psychoactive (mind-altering) drug use. In so doing, they attempt to answer questions such as: What does the fact of drug-induced mind-altering experiences tell us about natures of the mind, free will, and God? What does it tell us about what, and how, we can know? Are drug-induced mind-altering experiences valuable, morally, aesthetically, or otherwise? Is the acquisition of drug-induced mind-altering experiences ever immoral? Should the acquisition of drug-induced mind-altering experiences ever be legally prohibited? The Handbook gives an overview of the current research, and sets the stage for future directions in philosophical thought relating to psychoactive drug use.