Intraoperative neurophysiological monitoring (IONM) has become the gold standard for the monitoring of functional nervous tissue and mapping of eloquent brain tissue during neurosurgical procedures. The multimodal use of somatosensory-evoked potentials and motor-evoked potentials ensures adequate monitoring of anterior sensory and dorsal motor pathways. The use of IONM during spinal orthopaedic surgery has drastically reduced the incidence of postoperative neurological deficit and allowed radical resection of brain tumours. Evoked potentials (EPs) are analysed for increased latency (> 1 millisecond) and decreased amplitude (< 50%). Special considerations have to be made in the paediatric population who present with decreased myelination and morphological changes to the EPs. A thorough knowledge of the physics and physiology behind these techniques will ensure better outcomes and successful implementation in neurosurgical centres. In this two-part article series, we will provide a review of the most recent available literature on IONM. The different modalities that are available, their indications and application are presented in Part 1, while the different anaesthetic options that exist will be discussed and the basic approach to the planning of a successful anaesthetic outlined in Part 2.Keywords: evoked potentials, intraoperative monitoring, brain mapping