It is clear now that the two principal components of an animal’s temperature regulating capacity — central and peripheral — utilize catecholaminergic mechanisms. What is biologically so fascinating is the entirely different way in which a given catecholamine acts. On the one hand, central noradrenergic neurons are involved in the complicated activation of the processes underlying heat dissipation. But peripherally, the adrenergic principle is involved in the thermogenesis required for the defense against a cold environment. In this chapter, some of the principal findings will be presented that have provided the specific evidence upon which these viewpoints are now based.