“Osteogenesis imperfecta” is a term used to describe a group of genetic disorders of variable phenotype usually defined by recurrent fractures, low bone mass, and skeletal fragility. Most cases are associated with mutations in one of the type I collagen genes, but in recent years several other forms have been identified with recessive inheritance. In most instances the latter result from mutations in genes encoding proteins involved in type I collagen’s complex posttranslational modification or in genes regulating bone matrix homeostasis. This article reviews the recent discoveries and an approach to classification and diagnosis. Bisphosphonates are widely used in patients with osteogenesis imperfecta, but some important questions about their optimal usage, their utility in children and adults with milder phenotypes, and their potential adverse effects are not yet resolved.