Radiculopathy, a disorder of the spinal nerve roots, is one of the most common diagnoses referred for electrodiagnostic (EDX) evaluation. It is important to remember that an electromyography/nerve conduction study is an extension of the history and physical examination. EDX studies should be ordered when the diagnosis remains unclear. EDX studies functionally assess the nerve, localize the lesion, and exclude other neurological causes of limb pain, sensory changes, and weakness. Radiculopathy can be an axonal or demyelinating disorder affecting nerve fibers at the level of a single root or spinal nerve. The anterior (motor) root, posterior (sensory) root, or both may be affected. Pathology in the spinal nerve is less common. This chapter discusses lumbosacral radiculopathy and its clinical presentation, anatomy and electrodiagnostic approach.