Twenty years after its discovery, recombinant human leptin has been approved by the Food and Drug Administration for the treatment of patients with lipodystrophy. Beginning with a synthesis of the vast body of work on its discovery, dissection of mechanisms, and effects in experimental models , the focus of this book shifts to a consideration of the regulation and role of leptin in humans. The emphasis on human-level data is a unique feature of this book. The results of numerous studies indicate that leptin is indeed a regulated human hormone.