This issue of the American Journal of Medical Genetics Seminar Series Part C is dedicated to generalized joint hypermobility (gJHM), joint hypermobility syndrome (JHS), and Ehlers-Danlos syndrome, hypermobility type (EDS-HT). gJHM is the best known clinical manifestation of inherited defects of the connective tissue. On the other side, JHS and EDS-HT are actually considered one and the same from a clinical perspective by most practitioners and researchers (i.e., JHS/EDS-HT), and their molecular basis remains unknown. For decades, "non-syndromic" gJHM and JHS/EDS-HT have been thought to be simple clinical curiosities or an asset for the "affected" individual. In recent years, the attention on these partially overlapping phenotypes has increased, as they are now recognized risk factors for a series of non-communicable diseases and long-term disabilities. This series consists of 10 papers focused on three main topics, namely (i) assessment and differential diagnosis of children and adults with gJHM, (ii) systematic presentation of selected key non-articular manifestations of JHS/EDS-HT and actual perception of physiotherapy as the best therapeutic resource for this condition, and (iii) exploration of the available knowledge relating "congenital laxity of tissues" to various dysfunctions of the nervous system during development and adulthood. The contributors hope that this collection raises attention to this fascinating field of knowledge, which seems to have ramifications in virtually all medical disciplines.