Ultrasonography of shoulder joint recently enlarges its utility since the knowledge of the shoulder disease is increased by numerous researches. Ultrasonography is not only noninvasive, safe, and relatively cheap, but also an unique modality that can monitor tendon movement during shoulder motion. Sonographic examination generally starts from the front side of the shoulder joint and finishes at back side in sitting position. Many structures in shoulder joint such as muscles, ligaments, glenoid labrum, bone, and especially rotator cuff tendon can be examined by ultrasonography. The rotator cuff is a motion unit consisted with subscapularis, supraspinatus, infraspinatus, and teres minor muscles. It functions as fulcrum and compresses the humeral head onto the glenoid, and steers for shoulder joint.