Regional analgesia for arthroscopic or open surgical procedures requires accounting of the cutaneous, osseous and capsular innervation of the shoulder. A commonly used regional anesthetic technique, the interscalene block (ISB), anesthetizes the innervating nerves of the shoulder, with the goal of local anesthetic deposition in the vicinity of the C5-C6 nerve roots between the anterior and middle scalene muscle, also known as the interscalene groove. Besides optimizing postoperative pain, ISB can decrease patients’ recovery time in the postanesthesia care unit and length of hospital stay. Targeting the C5-C6 nerve roots allows analgesia of the axillary and suprascapular nerves which are primary in the innervation of shoulder joint. Additionally, the lateral pectoral, musculocutaneous and long thoracic nerves are anesthetized with the ISB providing complete anesthesia of shoulder. The phrenic nerve originates from the third, fourth and fifth cervical ventral rami with some contribution from the cervical sympathetic ganglia or thoracic sympathetic plexus. It originates near the roots of the brachial plexus, and courses over the lateral border of the anterior scalene muscle, posterior to the sternocleidomastoid muscle.