Abstract.Functional Near-Infrared Spectroscopy (fNIRS) is a non-invasive optical technique that measures cerebral hemodynamics across multiple regions of interest, and thereby characterises brain functional activation. Since its first description in 1993, fNIRS has undergone substantial developments in hardware, analysis techniques, and applications. Thirty years later, this technique is significantly enchancing our understanding in diverse areas of neuroscience research such as neurodevelopment, cognitive neuroscience, psychiatric disorders, neurodegenerative conditions, and brain injury management in intensive care settings. This special issue outlines the latest progress in instrumentation and analysis techniques and showcases some applications within the expanding field of fNIRS over the past decade.