A brief history of the evolution of radiculopathy as a clinical entity, and the use of electrodiagnostic studies to diagnose it, are provided. Root anatomy and the concept of myotomes and dermatomes are reviewed, as is the pathophysiology of radiculopathy. The value and limitations of the various electrophysiologic procedures used in the diagnosis of radiculopathies are discussed, including motor and sensory nerve conduction studies, late responses, somatosensory evoked potentials, nerve root stimulation, and the needle electrode examination. The specific muscles are enumerated which most often appear abnormal on needle electromyography with lesions of the various roots. The electrodiagnostic differentiation of root lesions from plexus lesions is described, and the various electrodiagnostic findings with lumbar canal stenosis are discussed. Finally, the value and limitations of the electrodiagnostic assessment in the evaluation of patients with suspected radiculopathies are reviewed.