Freiburg Optical NeuroImaging (FrONI) is a shared facility for near-infrared spectroscopy (NIRS) at the Medical Faculty of the University of Freiburg. The modularly scalable NIRS infrastructure available at FrONI allows spatially resolved topographic and tomographic NIRS measurements with up to several hundred channels. Methodologically established for this purpose are approaches to contrast agent-based measurements of cerebral blood flow, functional measurements of directional connectivity between brain areas, and functional measurements of task-associated brain activation. The mobile configuration of the NIRS unit allows it to be used in a wide variety of contexts, e.g. intra- and perioperative measurements in humans and animal models, monitoring on wards, functional experiments in the laboratory and even field studies in everyday settings, and also multi-modal measurements (e.g. with EEG, CT, or PET). FrONI is open to users of the University Medical Center and the University of Freiburg, as well as to external research groups and industrial users, and can support the design, implementation and analysis of NIRS studies.