Adipose tissue has recently been described as one of the major endocrine gland that plays a role in energy homeostasis, lipid metabolism, immune response, and reproduction. An excess of white adipose tissue, caused by a complex interaction between genetic, hormonal, behavioral, and environmental factors, results in obesity: a heterogeneous disorder that predisposes humans to a variety of diseases. Among several hormones, estrogens promote, maintain, and control the typical distribution of body fat and adipose tissue metabolism through still unknown mechanisms. These steroids are known to regulate fat mass, adipose deposition and differentiation, and adipocyte metabolism. Moreover, estrogen deficiency results in increases in adipose tissue, preferentially in visceral fat, which would link obesity to the susceptibility of related disorders. In this review the role of estrogens in adipose tissue differentiation and in the protection against the onset of obesity will be discussed with particular attention being drawn to the underlying molecular mechanisms mediated by estrogen receptor isoforms ERalpha and ERbeta.