The purpose of the book is to present the GAIRS (Global Assessment and Intervention in Rett Syndrome) Checklist, an easy-to-use, short and accessible tool for every health-care professional in order to assess all the abilities of Rett girls but also to identify patients needing next-step evaluation and treatment. Thanks to the hierarchical order of all the targets assessed in each area of the GAIRS, this checklist can be a useful instrument not only for assessment but also for intervention.