This volume explores research on marijuana-like substances produced naturally by the human body and brain. These endogenous lipid molecules, or endocannabinoids, constitute a uniquely conserved and ubiquitous physiological control system in a variety of species and plays fundamental roles in development and cell death. The authors discuss this remarkable progress in marijuana research including identification of genes encoding endocannabinoid receptors, isolation of endocannabinoids and entourage ligands, and functional identification of transporters and enzymes for the biosynthesis and degradation of these endogenous substances.