The present invention relates generally to glass compositions incorporating rare earth oxides. In one embodiment, a glass composition suitable for fiber forming comprises 51-65 weight percent SiO2, 12.5-19 weight percent Al2O3, 0-16 weight percent CaO, 0-12 weight percent MgO, 0-2.5 weight percent Na2O, 0-1 weight percent K2O, 0-2 weight percent Li2O, 0-3 weight percent TiO2, 0-3 weight percent ZrO2, 0-3 weight percent B2O3, 0-3 weight percent P2O5, 0-1 weight percent Fe2O3, at least one rare earth oxide in an amount not less than 0.05 weight percent, and 0-11 weight percent total other constituents. In some embodiments, the at least one rare earth oxide comprises at least one of La2O3, Y2O3, Sc2O3, and Nd2O3. The at least one rare earth oxide is present in an amount of at least 1 weight percent in some embodiments. The at least one rare earth oxide, in some embodiments, is present in an amount of at least 3 weight percent. The glass compositions can be used to form glass fibers which can be incorporated into a variety of other fiber glass products (e.g., strands, rovings, fabrics, etc.) and incorporated into various composites.