The general aim of the neurosurgical practice is to both anatomically and physiologically preserve functional neurological structures to ensure a higher quality of life. Intraoperative neuromonitorization (IONM) helps the neurosurgeon physiologically identify and assess the functional integrity of said neurological structures. The uses of IONM in neurosurgery practice are categorized into three areas; brain (supratentorial and infratentorial), brain stem, and spinal. For every anatomical region and surgical procedure, characteristic differences in electrophysiological methods exist for both recording and interpretation. In this first three-part paper, electrophysiological methods used in supratentorial surgeries for tumor, vascular, and epilepsy pathologies and their key points will be reviewed in detail. The second part uses infratentorial and brain stem surgeries; in the third part, uses in spinal surgery will be detailed.