Injuries or diseases of peripheral nerves can have severe impact on function, severe disability (inability to work), social and psychological effects or chronic pain. The main reason to perform Intraoperative monitoring (IOM) during peripheral nerve surgery are to prevent nerve injuries during surgery, to identify peripheral nerves or fascicles in cases of variable anatomy, scar tissue or tumors, to determine axon continuity across a lesion, and to guide surgical decisions regarding the type of neural reconstruction to perform. Nerve action potential (NAP) recording is considered a standard method for peripheral nerve monitoring given its ability to determine the presence or absence of functional axons in a segment of nerve, it also localizes functional and non-functional nerve segments. A NAP recording requires 4.000 to 5.000 intact or regenerating axons to be obtained and its preferred to compound muscle action potential (CMAP) recordings. The presence or absence of a NAP is more important than its latency, amplitude or shape. If a NAP is recorded in a nerve or fascicle, neurolysis is performed, and nerve grafts are required in no-responding fascicles. Some technical difficulties of NAP recording are related to very short stimulation/recording distances, stimulus artifact, volume conduction from another nerve, low temperature, use of tourniquet and use of local anesthetics. CMAP recording is like that used in triggered EMG, surface or subcutaneous needle electrodes are placed over desired muscles and the exposed peripheral nerve is stimulated. Free EMG is useful to detect, in real time, trains or bursts of abnormal discharges that indicate possible nerve damage. It́s easy to use, not affected by anesthesia and has high sensitivity but low specificity. Bipolar intramuscular electrodes are preferred for EMG recordings.