Evolutionary consideration and clinical observations led us to hypothesize 10 yr ago that there may be a coordinated regulation, endocrine in nature, of bone remodeling and energy metabolism. The existence of this coordinated regulation is motivated by the energetic needs of the skeleton; therefore, this regulation relies on hormones that appear during evolution with the skeleton, not with energy metabolism. Leptin is such a hormone, and it is a critical regulator of bone mass as well as of appetite and energy expenditure. This review goes over the anatomical route and molecular pathways used by leptin to inhibit both bone mass accrual and appetite through its signaling in the brain.