Adipose tissue was once considered a simple structure whose sole function was to store excess energy as fat. This view has changed radically in the recent past as it has been found to have additional and complex functions. Specifically, it has been shown to function as an endocrine tissue releasing adipokines that signal to other tissues, and as an inflammatory tissue releasing cytokines and related molecules. In this talk, factors regulating adipocyte number and function will be reviewed, and how these are altered in the obese state and contribute to the adverse health outcomes linked to obesity. The concept of metabolically healthy obesity will be considered, together with the recognition that too little adipose tissue can be just as bad as too much from the perspective of adverse health and increased disease risk.