In this chapter, discuss monitoring of neural function by using electrophysiologic techniques in the operating room (intraoperative monitoring) and briefly review the use of such techniques in the intensive care unit (ICU). IOM is used to identify an anatomical structure and early detection of intraoperative injury. Recordings are usually made over the scalp for analysis in SSEP, BAER, and VEP, while for MEP the recordings are made over various muscles. SSEPs are commonly used during carotid surgery, cerebral aneurysm surgery and manipulation of the spine and spinal cord during open or closed manipulation. Intraoperative BAER monitoring is routinely used in cerebellopontine angle or skull base surgery. VEP can be used as intraoperative monitoring modality for surgeries in the vicinity of the optic pathways. Direct mapping of the eloquent cortex is used to identify the important cortical function at the time of surgery and epilepsy surgery. EMG is used for cranial nerve localization, during selective dorsal rhizotomy and spinal tethered cord release. EMGs are unaffected by anesthetics, but requires absence of neuromuscular blockade. Continuous long-term EEG monitoring in various forms are used in neurointensive units in a variety of conditions including head trauma, intracerebral hemorrhage, subarachnoid hemorrhage, metabolic encephalopathies and nonconvulsive status epilepticus.