Near-infrared spectroscopy (NIRS) is a non-invasive optical technique that measures tissue oxygenation by detecting the absorption of near-infrared light by oxygenated and deoxygenated haemoglobin. It is clinically important for monitoring regional oxygen delivery and utilisation, particularly in critical care and during surgery, to prevent tissue hypoxia. A key application is in neonatal intensive care, where NIRS helps detect cerebral hypoxia and guide interventions to reduce the risk of brain injury.