A valuable classification system allows for communication among surgeons and/or other investigators and offers information on treatment and prognosis. It provides a means for comparison of epidemiologic data and treatment outcomes. There is no current standard classification for rotator cuff tears. Authors and practicing orthopaedists use a variety of descriptions when communicating about cuff tears. Older classifications do not use 3-dimensional information derived from the present use of arthroscopy and magnetic resonance imaging. The new geometric classification offers guidance on treatment and prognosis. Type 1, crescent-shaped tears are repaired end to bone and have a good to excellent prognosis. Type 2, longitudinal (L- or U-shaped) tears are repaired side to side with margin convergence and have a good to excellent prognosis. Type 3, massive contracted tears have coronal and sagittal dimensions greater than 2 x 2 cm on preoperative magnetic resonance imaging; are repaired with interval slides or partial repair; and have a fair to good prognosis. Type 4, rotator cuff arthropathy tears have end-stage degenerative changes of the glenohumeral joint and have articulation of the humeral head with the undersurface of the acromion; are irreparable; and require arthroplasty if surgery is considered. This classification describes complete tears of the superior and posterior rotator cuff, supraspinatus, infraspinatus, and teres minor. Additional notation can be made regarding the presence of related pathology including tears of the subscapularis, biceps, or labrum; instability or arthritic change of the glenohumeral or acromioclavicular joints; or fatty degeneration of the cuff.