Adaptive thermogenesis (AT) is the mass‐independent decrease in energy expenditure (EE) in response to caloric restriction and weight loss. AT becomes manifest throughout all periods of weight loss and persists during subsequent weight maintenance. AT occurs in resting and nonresting energy expenditure as ATREE and ATNREE, respectively. ATREE appears in different phases of weight loss, each with likely different mechanisms. By contrast, during weight maintenance after weight loss, ATNREE exceeds ATREE. Some of the mechanisms of AT are known now and others are not. Future studies on AT will need an appropriate conceptual framework within which to design experiments and interpret results.