The Atlas of X-Linked Intellectual Disability Syndromes is a comprehensive and up-to-date summary of the clinically distinctive disorders caused by genes on the X chromosome. Clinical and laboratory data on 150 syndromes are presented in a concise and consistent manner. Each syndrome is defined and information is provided on somatic features, growth and development, neurological signs, cognitive performance, imaging and other laboratory findings, and when possible, the nature and localization of the responsible gene. Craniofacial and other somatic findings are extensively illustrated. A differential matrix accompanies each syndrome description to assist the reader in identifying other X-linked syndromes with overlapping features. Individual syndrome entries are supplemented with nineteen appendices that identify syndromes with common features and provide the location or mapping limits and function of the responsible genes. The authors have extensive experience in the clinical and laboratory delineation of X-linked intellectual disability. They have described new syndromes, regionally mapped disease loci on the X chromosome, and identified the genes responsible for X-linked syndromes.