This article reviews the electrodiagnosis of brachial plexus injury, factors that predict outcome, the utility electrodiagnostic evaluation of potential nerve donors, and commonly used surgical interventions. Electrodiagnostic evaluation begins with a detailed understanding of brachial plexus anatomy and uses a complement of motor and sensory nerve conduction studies and needle electromyography to determine the location of injury and predict severity. Several factors are used to predict prognosis. In injuries with poor prognosis, surgical intervention is indicated. Nerve transfers are increasingly employed to improve functional outcomes. Electrodiagnosis is key to evaluating the viability of potential nerve donors.