Adrenergic stimulation of brown adipose tissue (BAT) induces acute and long-term responses. The acute adrenergic response activates thermogenesis by uncoupling oxidative phosphorylation and enabling increased substrate oxidation. Long-term, adrenergic signaling remodels BAT, inducing adaptive transcriptional changes that expand thermogenic capacity. Here, we show that the estrogen-related receptors alpha and gamma (ERRα, ERRγ) are collectively critical effectors of adrenergically stimulated transcriptional reprogramming of BAT. Mice lacking adipose ERRs (ERRαγAd-/-) have reduced oxidative and thermogenic capacity and rapidly become hypothermic when exposed to cold. ERRαγAd-/- mice treated long term with a β3-adrenergic agonist fail to expand oxidative or thermogenic capacity and do not increase energy expenditure in response to norepinephrine (NE). Furthermore, ERRαγAd-/- mice fed a high-fat diet do not lose weight or show improved glucose tolerance when dosed with β3-adrenergic agonists. The molecular basis of these defects is the finding that ERRs mediate the bulk of the transcriptional response to adrenergic stimulation.