The knee plays a significant role in ambulation and the activities of daily living. During the course of these activities and its role in weight bearing, the knee is susceptible to a variety of different forces and the emergency physician should be familiar with the diagnosis and treatment of the injuries that result. In addition to following basic trauma protocols, thorough neurovascular and musculoskeletal examinations should be performed and supplemented with appropriate imaging. Emergency physicians should also consider recent developments in knee anatomy and function when evaluating the patient with an acutely injured knee.