Abstract Neurophysiological investigations are primarily requested by orthopaedic surgeons in order to investigate sensory or motor dysfunction in the limbs. They often wish to substantiate their clinical diagnosis before proceeding with surgery, or to confirm a nerve injury. A diagnostic query adequately supported by relevant history and examination is essential to determine the type of neurophysiological investigation required to support the diagnosis. A basic understanding of the available investigations, their indications and limitations, is useful to the surgeon for interpretation of the results in light of the clinical picture. Underpinning all neurophysiological investigations is the knowledge of the basic anatomy and physiology of the nervous system. We discuss the generation and propagation of action potentials, which can be generated by the electrical stimulation of a peripheral nerve and responses may be recorded along the course of the nerve or from the muscle (nerve conduction studies). Electrical activity from a muscle can also be recorded with a needle electrode (electromyography), whilst a stimulus in a peripheral sensory nerve can be recorded in the spinal cord or brain (somato-sensory evoked potentials). We discuss the aforementioned tests, looking at the indications for their use. Normal patterns of results as well as those that would be considered to be pathological will also be discussed.