Fentanyl is an important highly lipid-soluble and potent piperidine opioid analgesic frequently administered for acute and chronic pain management, particularly for severe and chronic pain. This chapter introduces fentanyl within the context of both acute and chronic pain management, examining impact and implications in the broader ongoing opioid epidemic. We provide a review of pharmacology, indications, uses, dosage forms, efficacy, and side effects of fentanyl, along with important considerations for clinical application. Fentanyl pharmacokinetics and pharmacodynamics, including interaction with μ-opioid receptors and rapid onset of action, are described. Analgesic-mediated mechanisms not only provide superior analgesic properties but also can result in increased risk for misuse and addiction. Its effectiveness includes a rapid onset and various formulations, such as intravenous, transdermal patches, and transmucosal delivery systems, as well as a role in managing surgical and breakthrough pain. The risks of respiratory depression and overdose associated with fentanyl are also addressed, especially in the context of illicit use in the opioid epidemic. Considerations for management of common side effects like nausea, constipation, and potential overdose are presented, with particular emphasis on the role of naloxone in reversing fentanyl-induced respiratory depression. Recent clinical studies are summarized to provide insight into safety and efficacy across diverse populations and clinical conditions, demonstrating a critical role in improving quality of life for patients suffering from severe pain. This chapter offers a comprehensive resource on its role in pain management to support informed and responsible use in medical practice, addressing its powerful analgesic properties and crucial safety measures required to prevent harm.