Over the past decade, the understanding of the processes involved in the regulation of gonadotropin-releasing hormone and its dysfunction has greatly increased. As new regulatory peptides have been identified, the underlying causes of central hypogonadism have multiplied, and the area has become increasingly complex. The reversibility of even genetically determined hypogonadotropic hypogonadism has become more firmly established, and clinical studies have greatly expanded our understanding of basic physiological pathways. Structuring this mass of new knowledge in thirteen comprehensive chapters, a group of renowned experts, representing the principal international research groups, take stock of the most recent progress. This up-to-date overview helps scientists and clinicians to plan future research and treat patients with delayed puberty, hypogonadotropic hypogonadism and other forms of central reproductive disorders.