Uncoupling protein (UCP) is essential to the thermogenic function of brown adipose tissue (BAT). The thermogenic role of this protein is due to its capacity to uncouple oxidative phosphorylation in a regulated manner. The thermogenic potential of BAT is determined by its content of UCP. The gene encoding this protein is under complex regulation. Catecholamines, via cAMP, thyroid hormone and retinoic acid, directly stimulate the gene acting upon an upstream (−2·28/−2·49 kb) enhancer sequence, but cAMP may act upon other sequences of the gene as well. CCAAT enhancer binding proteins and peroxisome proliferation activator receptor (PPAR)γ2 have also been implicated in the regulation of the gene acting on discrete sequences. While the thyroid hormone response and retinoic acid response elements (TRE and RARE) have been well defined, the cAMP response elements (CRE) remain elusive. The two TREs are 27 bp apart between −2·33 kb and −2·39 kb. The synergism between cAMP and thyroid hormone seems to reside in a 39 bp sequence downstream (−2·28/−2·32 kb). The most important CRE, the RARE, a cell-specific enhancer and a putative PPAR element are all concentrated in a 90 bp regulatory element of great complexity (−2·40/−22·49 kb). Other hormones, such as insulin and glucocorticoids, and IGF-I also modulate the expression of the gene but their effects seem to be largely indirect. Understanding the regulation of the UCP gene expression may facilitate the development of interventions in obesity and related disorders.