In recent days functional near-infrared spectroscopy (fNIRS), which is non‐invasive, portable, affordable, safe, easy-to-use device that does not expose people to radiation, has become popular as an emerging optical imaging technique for studying human brain function. It has significantly contributed to the understanding of neural correlates. These advantages make it especially useful in the investigation of neurological disorders. However, fNIRS has still not become prevalent compared to other neuroimaging techniques in the field of Neurology. For this reason, the purpose of this review article is to introduce fNIRS techniques and report fNIRS studies in the field of Neurology. In addition, the basic principles of fNIRS, including the features, advantages, and limitations are summarized in the review.