The most common presenting complaint to the emergency department (emergency room) is pain. Unfortunately, pain is still undertreated in this setting. Literature has shown that treatment of pain not only improves patient satisfaction but also improves mood, decreases length of hospital stay, and decreases mortality. Various pharmacological options are available for treating acute pain, ranging from oral, intravenous, and intramuscular medications; topical agents; and peripheral nerve blocks. Objectively assessing and documenting a patient's pain is the key to determining treatment. The approach to a patient with acute pain requires an experienced clinician who is aware of the pharmacology of analgesics and anesthetics, contraindications, precautions, side effects, administration methods, and monitoring requirements.This chapter briefly covers the pathophysiology of acute pain and the different treatment modalities available to the emergency physician.