Leptin is an adipocyte-derived hormone with an important role in the central control of energy metabolism and with many pleiotropic effects in different physiological systems. One of these is the regulatory role between energy metabolism and the immune system, being a pillar in the new concept of immunometabolism. Leptin receptor, expressed overall in the immune system, acts in both innate and adaptive immune system cells. As an adipokine, leptin is responsible for the inflammatory state found in overnutrition. Moreover, in undernutrition status, it plays as crucial mediator of the immunosuppressive state.