Systems and methods for performing optical spectroscopy using a self-calibrating fiber optic probe are disclosed. One self-calibrating fiber optic probe includes a sensing channel for transmitting illumination light to a specimen and for collecting spectral data of the specimen. The spectral data includes the illumination light diffusely reflected from the specimen at one or more wavelengths. The self-calibrating fiber optic probe may also include a calibration channel for transmitting calibration light. The calibration light and the illumination light are generated simultaneously from a common light source. The calibration channel collects calibration spectral data associated with the calibration light contemporaneously with the collection of the spectral data of the specimen.