Obesity is correlated with low-grade inflammation, which provides a potential link between insulin resistance and the endothelial dysfunction present in the early stages of the atherosclerotic process. Adipose tissue has been considered until recently, just a depot for energy storage, which has the sole function of accretion in the form of triacylglycerols of excess energy. However, adipose tissue is now considered an active endocrine organ that releases a wide range of endocrine, paracrine and metabolic signals. Although obesity increases in adipose tissue the expression of genes is related with inflammation and immunity (and, conversely, caloric restriction improves this inflammatory profile), these genes are expressed mainly in the cells of the stromal vascular fraction of the adipose tissue rather than in the adipocytes. Adipose tissue structure is not uniform. More than half of the adipose tissue cells belong to a heterogeneous stromal vascular fraction, which includes stem cells, preadipocytes, endothelial cells, and macrophages. The strong relationship between adipose tissue, macrophage content and the indicators of adiposity hit at their implication in the increased adipose tissue production of proinflammatory molecules and acute phase proteins associated with obesity. The growing knowledge of the implication of adipose tissue in inflammation, response to immune challenge, and tissue proliferation may be directly traced to cell types not directly related to the energy storage function. Thus, we can conclude that white adipose tissue is something more than simply adipocytes.