The shoulder is the most complex joint in the body. It is capable of moving in more than 16,000 positions. Many of its disorders, including the most common ones, involve specific biomechanical mechanisms of the shoulder. The most common shoulder problem for which professional help is sought is shoulder impingement (Haig 1996). Shoulder impingement is primarily an overuse injury involving mechanical compression of the supraspinatus tendon, subacromial bursa, and tendon of the long head of the biceps, all of which lie beneath the coracoacromial arch (Prentice 2001). Impingement has been described as a continuum during which repetitive compression ultimately leads to irritation and inflammation that progresses to fibrosis and ultimately rotator cuff tear. Because impingement involves a spectrum of shoulder tissue injuries, a working knowledge of its structural relationships will facilitate understanding of the factors causing abnormalities. This article will provide knowledge on the anatomy, biomechanics, and proper rehabilitation involved in shoulder impingement. Impingement syndrome was originally described by Dr. Charles Neer as mechanical impingement of the supraspinatus muscle and the long head of the biceps tendon beneath the acromial arch. Neer classified three phases of the conflict. Stage I is characterized by edema and hemorrhage of the rotator cuff and suprahumeral tissue. Stage II is characterized by fibrosis of the glenohumeral capsule and subacromial bursa and tendinitis of the involved tendons. Patients usually show a loss of active and passive range of motion due to capsular fibrosis. Stage III is the most difficult to treat and is characterized by rupture of the rotator cuff tendons. This includes rotator cuff tears, biceps tears, and bone changes. Because this is an ongoing disease process, there is often overlap in signs and symptoms (Hawkins and Abrams 1987). For descriptive purposes, factors related to shoulder impingement can be divided into intrinsic and extrinsic categories. Intrinsic factors directly involve the subacromial space and include changes in the vasculature of the rotator cuff, degeneration, and anatomical or bony abnormalities. Extrinsic factors include muscle imbalances and motor control problems of......middle of article......Blackwell.Haig, S. (1996). Rehabilitation and pathophysiological treatment of the shoulder. Gaithersburg, MD: Aspen. Hawkins, R., & Abrams, J. (1987). Impingement syndrome in the absence of rotator cuff tear (stages 1 and 2). Orthopedic Clinics of North America, 18, 473.Kibler, W., McMullen, J., Uhl, T. (2001). Strategies, guidelines and practice for shoulder rehabilitation. Orthopedic Clinics of North America, 32, 527.Pecina, M., & Bojanic, I. (1993). Overuse injuries of the musculoskeletal system. Boca Raton: CRC Press. Placzek, J., & Boyce, D. (2001). Secrets of orthopedic physiotherapy. Philadelphia: Hanley & Belfus, Inc. Prentice, W. (2001). Musculoskeletal rehabilitation techniques. New York: McGraw Hill.Shamus, E., & Shamus, J. (2001). Sports injury: prevention and rehabilitation. New York: McGraw-Hill. Taylor, J., & Taylor, S. (1997). Psychological approaches to the rehabilitation of sports injuries. Gaithersburg, MD: 1997.