The basal joint complex of the thumb provides the framework necessary for function of the human hand. Although its unique saddle articulation allows for a wide range of motion necessary for routine function of the hand, it is rendered inherently unstable because of poor bony congruency and reliance on its capsuloligamentous support. Painful instability of this joint can stem from several causes including traumatic dislocation, various hypermobility conditions, and chronic overuse and microtrauma. A thorough history and examination as well adequate imaging is necessary for proper evaluation of instability. Treatment options range from nonoperative modalities to surgery, which entails closed, percutaneous, or open reduction with numerous ligament repair and reconstruction techniques. Arthroscopy can also serve to be a useful adjunct for assessment of the joint and stabilization of the critical capsuloligamentous structures. This review outlines the critical osseous and soft-tissue anatomy surrounding the thumb carpometacarpal joint, the key points in evaluating patients presenting with acute traumatic and chronic thumb carpometacarpal instability without fracture or arthritis, and reviews both nonoperative and operative treatments of this injury.