The ulnar collateral ligament (UCL) is commonly injured in sports that require an overhead motion, such as throwing a ball. This imparts a valgus stress upon the elbow, which is resisted by the UCL. However, repeated or excessive stress to the ligament may result in injury to the ligament. Injury to the UCL may result in secondary injury to other areas of the elbow, including the ulnar nerve, the flexor–pronator musculotendinous unit, the radiocapitellar joint, and the posterior compartment of the elbow, in addition to being the cause of loose bodies within the elbow. This manuscript briefly reviews the anatomy, biomechanics, and pathophysiology of injury to the UCL and injuries to the other structures that are a direct result of UCL injury. Further, this paper discusses the patient's history, examination techniques, and tests that help confirm the diagnosis of UCL injury. Lastly, it discusses the treatment of UCL injury.