The functional anatomy of the rotator cuff and its relationship to the mechanism of shoulder joint movements and control is now becoming more clearly understood. Common variations in the anatomy of the acromion and the subacromial region, particularly the coraco-acromial ligament, and its relationship to the tendon of the supraspinatus are now seen to be major determinants of degenerative changes in the rotator cuff. Changes in the matrix of the musculotendinous region, which may be related to mechanical interference with the vascular supply to the tendon are now a possible determinant of early degenerative changes (both primary, and those secondary to trauma) in the rotator cuff. The relationship of these findings to the management of lesions of the rotator cuff is discussed.