This chapter discusses disorders caused by disorganization of skeletal constituents and includes discussion on fibrous dysplasia, cherubism, progressive osseous heteroplasia, multiple cartilaginous exostoses, osteoglophonic dysplasia, fibrodysplasia ossificans progressiva, enchondromatosis, metaphyseal chondromatosis with 2-hydroxyglutaric acidura, genochondromatosis, and metachondromatosis. Each discussion includes major radiographic features, major clinical findings, genetics, major differential diagnoses, and a bibliography.