Adipose tissue is not only a reservoir for energy, but also an immune organ. In the context of obesity, the development of insulin resistance is now recognised to be initiated by inflammation of the adipose tissue. However, the primary events triggering this inflammation are still unclear, as a complex combination of endocrine and immune factors act to regulate this adipose tissue microenvironment. Below we discuss the different factors involved and how they affect the biology of the adipose tissue in obesity.