Optical coherence tomography (OCT) is a 3-dimensional high-resolution imaging modality based on an interferometry and is widely used in a large variety of medical fields. Spectroscopic OCT (S-OCT) is a signal-processing method that uses the raw interferograms generated by OCT to investigate depth-resolved spectroscopic profiles of a sample. The spectroscopic information provided by S-OCT can be used to enhance the contrast of OCT images and overcome the limitations of gray-scale OCT images that describe only morphology. In this review, we present the concepts behind S-OCT as well as acquisition methods and description of obtainable spectroscopic properties. Furthermore, this review covers the biomedical applications of the spectroscopic information that can be obtained with S-OCT, including measurements of hemoglobin concentrations, blood oxygen saturation levels, atherosclerotic plaque detection, evaluation of burn injuries, contrast enhancement using exogenous contrast agents, and detection of precancerous lesions.