In brief:Specific diagnosis of an athletic injury to the knee can be difficult if based on history and clinical examination alone. In some cases, arthrography has been used to aid in diagnosis; however, the arthrogram—though accurate—has several disadvantages, including the need for injection of contrast material and exposure of the patient to ionizing radiation. A noninvasive and highly accurate alternative for assessing selected knee injuries is magnetic resonance imaging (MRI). The authors briefly review the theory behind MRI, the history of its development, and its specialized terminology; they describe the procedure, the types of pathologic conditions MRI can demonstrate, and its clinical applications in knee injuries.