Carpal instability is defined as the pain and dysfunction of the wrist due to the anatomical and biomechanical change of the joint resulting from the injury of the ligaments between the carpal bones. Untreated carpal instability leads to degenerative arthritis of the wrist. In the past, the diagnosis and treatment of the fractures of this area were emphasized alone. However, today, we can mention the necessity of the investigation of a carpal instability and a proper treatment plan in cases of painful wrist. In this review, the etiology, classification and diagnosis of carpal instability were summarized.