Intraoperative neurophysiology (ION) plays a crucial role in dorsal rhizotomy, a procedure aimed at reducing spasticity while preserving neural function. ION encompasses monitoring and mapping, with the mapping of the root/rootlet constituting a significant component. Despite the acknowledged roles of ION, persistent controversies exist, and a universally accepted standard for integrating ION procedures into dorsal rhizotomy remains elusive. This chapter provides a detailed explanation of the author’s approach to dorsal rhizotomy, with a primary focus on the decision-making process for root/rootlet cutting. This process involves tetanic electrical stimulation of dorsal root/rootlet for rhizotomy, pudendal mapping to prevent urological complications, and monitoring the bulbocavernosus reflex (BCR). Additionally, the chapter introduces the use of the F-wave for assessing spasticity. The author terms this ION-guided dorsal rhizotomy as “functional posterior rhizotomy,” signifying a shift toward a more functionally oriented procedure extending beyond root selection. The application of ION in this procedure is systematic, ensuring both spasticity reduction and the preservation of urinary function. Decision-making for root/rootlet cutting is a multifactorial process, incorporating ION results, spasticity distribution, patient age, and preoperative function. This functional approach aims to minimize the cutting rate through the comprehensive utilization of ION procedures and a cutting rate formula correlating with the GMFM-88 score. In conclusion, ION proves integral to dorsal rhizotomy, facilitating functional root/rootlet selection for spasticity reduction, preserving neural function, and offering predictive insights into surgical outcomes.