The acromioclavicular (AC) joint may be affected by a number of pathologic processes, most commonly osteoarthritis, posttraumatic arthritis, and distal clavicle osteolysis. The correct diagnosis of a problem can usually be deduced from a thorough history, physical examination, and radiologic evaluation. Asymptomatic AC joint degeneration is frequent and does not always correlate with the presence of symptoms. Selective lidocaine injection enhances diagnostic accuracy and may correlate with surgical outcome. Nonoperative treatment is helpful for most patients, although those with osteolysis may have to modify their activities. In appropriately selected patients, open or arthroscopic distal clavicle resection is necessary to relieve symptoms. Recent biomechanical and clinical data emphasize the importance of capsular preservation and minimization of bone resection; however, the optimal amount of distal clavicle resection remains elusive. Patients with AC joint instability have poor results after distal clavicle resection.