Adipose tissues are the major organ that controls systemic energy metabolism and maintain homeostasis by storing lipids, dissipating them as heat, and producing various adipokines. There are two major classes of adipocytes: white and brown adipocytes. White adipocytes store and release lipids, while brown adipocytes burn substrates to produce heat. In addition to classical brown adipose tissues consisting of brown adipocytes, cold exposure and β3 stimulation induce development of brown cell-like "beige" adipocytes in white adipose tissues. There appear to be multiple adipocyte progenitor cell populations of different developmental origins. In this article, we overview white and brown/beige adipocyte differentiation in development and obesity. Adipocytes differentiate in complex interplays with various stromal cells, including vascular, immune and neuronal cells. Elucidation of the cellular interplays would lead to identification of novel therapeutic targets for obesity and metabolic syndrome.