This chapter summarizes knowledge of catechoaminergic innervation of the diencephalon of various mammalian species as of the early 1990s. Topics include: 1) the distribution of neuronal catecholaminergic groups, 2) the distribution of catecholaminergic fibers, 3) the morphological relationships with other neuronal systems, and 4) the functional implications of such relationships. The distribution of neuronal catecholaminergic groups is illustrated in coronal and saggital diagrams of several species including sheep, cats, rodents, humans and nonhuman primates.