Swimmer's shoulder is a broad term often used to diagnose shoulder injury in swimmers. However, research has elucidated several specific shoulder injuries that often are incurred by the competitive swimmer. Hyperlaxity, scapular dyskinesis, subacromial impingement, labral damage, os acromiale, suprascapular nerve entrapment, and glenohumeral rotational imbalances all may be included within a differential diagnosis for shoulder pain in the competitive swimmer. An understanding of the mechanics of the swim stroke, in combination with the complex static and dynamic properties of the shoulder, is essential to the comprehension and identification of the painful swimmer's shoulder. It is important for the athlete, coach, and clinician to be aware of the discerning characteristics among these different injuries to ensure a proper diagnosis and treatment plan to aid the swimmer in his or her return to competition.