Anterior glenohumeral instability is a common, yet complicated orthopaedic disorder. During the past few years, basic science research has improved the understanding of the glenohumeral joint stabilizing systems. The current authors review new contributions specifically detailing study of the interplay between the static and dynamic restraints. Simulation of the shoulder muscles in a recent study also has manifested the powerful contribution of the joint reaction force to concavity-compression. Continued advances, such as these, will improve the understanding, and allow better outcome, in treatment of glenohumeral instability.