Theories about the etiologies of anterior and lateral shoulder pain have changed greatly since "impingement disease" was first described. It is thought that such pain may be caused by contact between the rotator cuff and the acromion and coracoacromial ligament, but the exact pathophysiology of rotator cuff disease remains unclear. The shoulder is notoriously difficult to examine because of the variability of the physical findings in patients with rotator cuff disease. New concepts of impingement, such as coracoid impingement and internal impingement, have been advanced. Although no test is definitive for all causes of anterior and lateral shoulder pain, as the pathophysiology of these conditions becomes better understood the ability to evaluate them clinically also improves.