The glenohumeral joint is composed of the glenoid (socket), the humeral head (ball) and the capsule or ligaments that surround it. It allows the arm to move in many directions.

The glenoid is the "socket" of the shoulder blade (scapula). The humeral head or "ball" sits in the glenoid much like a golf ball sits on a tee. A rim of tissue called the labrum helps deepen its surface.