The use of opioids to manage immediate postoperative pain is frequently associated with nausea, vomiting, respiratory depression, hormonal effects and dysphoria. As such, achieving pain control while minimizing opioid use is critical, since more than 60% of unplanned prolonged hospitalizations and hospital readmissions are thought to be related to inadequate pain control or to side effects of opioids. A number of techniques have been used to achieve good pain control after arthroscopic shoulder surgery, including periarticular infiltration (PAI) with local anesthetic (LA) and regional anesthetic nerve blocks. Although PAI in the shoulder has been shown to decrease shoulder pain and opioid consumption, it is not as effective as regional blocks such as the interscalene nerve block (ISNB), which is the current gold standard. Nevertheless, the ISNB is potentially associated with significant side effects including persistent neurologic complications, rebound pain, phrenic nerve palsy, respiratory distress, cardiac arrest pneumothorax and central nerve toxicity. In view of this, investigating alternate regional blocks having the potential for good pain relief with minimal side effects is important. The Erector Spinae Plane (ESP) block can be considered as a modification of thoracic paravertebral block (PVB) that blocks thoracic spinal nerves using injections outside of the conventional paravertebral space. It is performed under ultrasound (US) by injecting local anesthetic deep to the erector spinae muscle at the interfascial space between either the erector spinae muscle and the rhomboid major muscle (higher up), or between the erector spinae muscle and the external intercostal muscles, at lower sites. Cadaveric studies of ultrasound-guided ESP blocks with methylene blue dye and subsequent dissection, as well an ESP block with a dye mixture and CT scanning demonstrated that when injecting deep into the erector spinae, the block likely affects the ventral and dorsal rami leading to the sensory blockade. The advantages include its simplicity and safety by limiting the risk of nerve damage and pneumothorax. Various case reports have demonstrated the ESP block to be successful for abdominal, breast and axillary, and other surgery types, and a recent case report described the successful management of chronic shoulder pain without motor blockade, with ESP performed at T3 level. The investigators conducted a systematic review via Pubmed to identify studies that have utilized ESP for post-surgical shoulder pain. Out of 77 reports, the investigators did not identify any comparative studies looking at the potential of ESP for shoulder surgery pain. The investigators also looked into ongoing and proposed trials of ESP by looking into clinicaltrials.gov. The investigators identified 21 studies including some randomized controlled trials (RCT) for thoracic surgery and general surgery population, but none for shoulder surgeries. Given the importance of providing adequate analgesia for arthroscopic shoulder surgery and lack of consensus amongst surgeons and anesthesiologists for the optimal analgesic technique, this trial will help establish the effectiveness of the ESP block in pain control after shoulder arthroscopy and define its safety profile. The results of this trial will allow the clinician to inform patients accurately regarding the benefits and risks of the block and thus guide the clinical practice of this block for shoulder arthroscopy. If proven to be effective, it may be used as an alternative to ISNB, especially in cases where ISNB is contraindicated.