Hundreds of thousands of asteroids have been discovered in the asteroid belt and in near-Earth space. Oxygen is an abundant element in meteorites and presumably in most asteroids. Spectral reflectance measurements of asteroids in the visible and near-infrared can identify oxygen-bearing minerals such as those found in the olivine, pyroxene, and serpentine groups due to their distinctive absorption features. Interpretation of the mineralogy of asteroids is complicated by the effects of space weathering, which tends to redden and darken the surfaces of asteroids. Asteroids are primarily classified into a number of taxonomic classes and subclasses according to their spectral properties in the visible wavelength region. However, asteroids with similar spectral properties in the visible may have different spectral properties in the near-infrared and, therefore, different interpreted mineralogies. Definite trends in the abundances of different taxonomic classes versus heliocentric distance are apparent. These trends appear to be a function of both composition differences and degree of heating. However, dynamical processes have significantly affected these trends. Close observation of asteroids by spacecraft, such as NEAR-Shoemaker to 433 Eros and Hayabusa to 25143 Itokawa, are currently the best way to discern the mineralogies of individual asteroids.