This chapter compares the distribution of catecholaminergic cell groups, i.e., clusters of cells fluorescent for dopamine, epinephrine or norepinephrine, in the diencephalon, midbrain and hind brain of a variety of mammals. Cell groups A1- A14 are compared and contrasted in human, monkey, rabbit, guinea pig, hamster, mouse, cat, dog, sheep, domestic pig and cow.