One of the most common complications of thyroid surgery is recurrent laryngeal nerve (RLN) injury. The gold standard to minimize the risk of RLN palsy is visual identification and careful dissection. However, most of the RLN injury is functional and occurs in anatomically integral nerves. Over the past two decades, intraoperative nerve monitoring (IONM) has become a powerful tool to preserve the RLN and to predict intraoperatively its functionality. IONM allows RLN identification, mapping, and dissection, helping the surgeon particularly in difficult cases, such as thyroid malignancies, mediastinal goiter, thyroid reoperation, and in presence of anatomical variations of RLN. The IONM ability to prevent RLN injury has been evaluated in several studies and meta-analysis, but with controversial results. Overall, IONM seems to significantly reduce the ILN injury rate in difficult cases such as malignant diseases and when thyroidectomy is performed by low-volume surgeons. Moreover, IONM has the potential to identify and test the functionality also for the external branch of the superior laryngeal nerve (EBSLN). Finally, IONM predicts postoperative vocal fold function, allowing the surgeon to delay completion surgery on the other side until nerve function has recovered, thus mitigating the risk of bilateral vocal fold palsy. The rationale of IONM and the benefits of its use during thyroidectomy have been presented in this chapter.