The shoulder joint is a complex structure composed of intricate bony architecture and an ornate system of muscles, tendons, and ligaments. What many refer to as the "shoulder joint" is actually a combination of 4 articulations--the glenohumeral joint, acromioclavicular joint, sternoclavicular joint, and the scapulothoracic articulation. These structures work together to provide the shoulder complex with multiple degrees of freedom, which allow the upper extremity to be abducted, adducted, rotated, flexed, and extended. Although this flexibility is vital for positioning the arm in space, it can make the evaluation of pathology difficult. Furthermore, neck pathology can refer pain to the shoulder, which may require a screening evaluation of the neck. This article reviews the relevant anatomy and discusses an approach to the differential diagnosis of shoulder pain.