Brown adipose tissue (BAT), a specialized fat that dissipates energy to produce 
heat, plays an important role in the regulation of energy balance. Two types of 
thermogenic adipocytes with distinct developmental and anatomical features exist 
in rodents and humans: classical brown adipocytes and beige (also referred to as 
brite) adipocytes. While classical brown adipocytes are located mainly in 
dedicated BAT depots of rodents and infants, beige adipocytes sporadically 
reside with white adipocytes and emerge in response to certain environmental 
cues, such as chronic cold exposure, a process often referred to as "browning" 
of white adipose tissue. Recent studies indicate the existence of beige 
adipocytes in adult humans, making this cell type an attractive therapeutic 
target for obesity and obesity-related diseases, including type 2 diabetes. This 
Review aims to cover recent progress in our understanding of the anatomical, 
developmental, and functional characteristics of brown and beige adipocytes and 
discuss emerging questions, with a special emphasis on adult human BAT.