: Excessive daytime sleepiness (EDS) is a common symptom of sleep disorders such as narcolepsy, obstructive sleep apnea, and hypersomnia. The most common tools for assessing EDS are various specialized questionnaires such as Epworth Sleepiness Scale (ESS) and Stanford Sleepiness Scale (SSS). However, the scores obtained from self-rating questionnaires do not seem to measure physiological sleepiness but rather a more complex phenomenon of subjective sleepiness modulated by other factors such as motivation, expectation, and capability of self-perception. The golden standard for measuring physiological sleepiness and assessing EDS is the Multiple Sleep Latency Test (MSLT). However, MSLT is very time consuming and requires trained personnel and expensive equipment. Different method modifications are employed in various medical and industrial fields for different purposes. The infrared pupillography in darkness has the potential to measure objective physiological sleepiness, especially the Pupillographic Sleepiness Test (PST), which is the method of choice for pupillographic measurement of daytime sleepiness. The method has also been employed in several specific sleep disorders, outlining possible future usage. This narrative review summarizes the current state of knowledge on the relevance and usefulness of pupillography in sleep medicine.