Electrodiagnostic medicine (EDX) should be considered an extension of a comprehensive patient history and physical examination. Combining data found on nerve conduction studies and needle electromyography, the pathophysiology of a peripheral nerve disease process can be further defined to illustrate location, duration, severity, and prognosis. It can function as a valuable aid in patient management, serving as an extension of the clinical exam, but not a substitute. This chapter focuses on board-related topics about EDX medicine as well as neuromuscular disorders and their associated electrophysiologic changes. It discusses basic peripheral nervous system anatomy followed by the pathophysiology, clinical instrumentation, nerve conduction studies and somatosensory evoked potentials. Then it describes basic needle EMG, radiculopathy, plexopathies, upper limb mononeuropathies, lower limb mononeuropathy, peripheral neuropathies, neuromuscular junction disorders, myopathies, motor neuron disease and differential diagnosis of weakness.