The shoulder is located where the humerus (upper arm), clavicle (collarbone), and scapula (shoulder blade) meet. While many people think of the shoulder as a single joint, the shoulder actually has four joints:

The glenohumeral joint is the major joint in the shoulder, where the rounded top, or head, of the humerus, nestles into a rounded socket of the scapula, called the glenoid. This ball-and-socket construction allows for circular movement of the arm.

The acromioclavicular joint is located where the collarbone, or clavicle, glides along the scapula’s acromion. The acromion is at the highest point of the scapula, which is an irregular, somewhat flat, triangle-shaped bone. The acromioclavicular joint facilitates raising the arm over the head.

The sternoclavicular joint is located where the clavicle meets the sternum at the top of the chest.

The scapulothoracic joint is sometimes considered a joint. It is located where the scapula glides against the thoracic rib cage at the back of the body. No ligaments connect the bones at this joint.