Endocannabinoids were defined in 1995 as endogenous agonists of cannabinoid receptors, i.e. of the G protein-coupled receptors for cannabis's psychoactive principle, Delta9-tetrahydrocannabinol. Although there appear to be several endocannabinoids, only two of such endogenous mediators have been thoroughly studied so far: anandamide and 2-arachidonoylglycerol (2-AG). A general strategy seems to apply to the biosynthesis and degradation of anandamide and 2-AG, although the levels of these two compounds appear to be regulated in different, and sometimes even opposing, ways. "Endocannabinoid enzymes", that is to say enzymes that catalyse endocannabinoid biosynthesis or degradation, have been identified and in some cases cloned, and will be described in this review together with their possible pharmacological targeting for therapeutic purposes. The cellular and subcellular localization and the modes for the regulation of the expression and activity of these enzymes play an important role in the functions played by the endocannabinoids under physiological and pathological conditions.