Intraoperative neuromonitoring is a perioperative method, supplementary to stealth navigation and fluorescence microscopic imaging in brain surgery. It allows cortical and subcortical mapping, hence real time identification of eloquent brain areas through electrical stimulation of the cerebral cortex and subcortical areas. The method allows for functional guidance during both awake and asleep neurosurgery and aids in optimizing the extent of resection of the relevant pathology while preserving neurological function as summarised in this review.