The present invention relates generally to glass compositions incorporating rare earth oxides (RE2O3). In one embodiment, a glass composition suitable for fiber forming comprises 51-70 wt. % SiO2, 12.5-22 wt. % Al2O3, 0-20 wt. % CaO, 0-11 wt. % MgO, 0.2-1 wt. % Fe2O3, 0.05 or greater wt. % RE2O3, and greater than 1 wt. % MnOx. In another embodiment, a glass composition suitable for fiber forming comprises 51-70 wt. % SiO2, 12.5-22 wt. % Al2O3, 0-20 wt. % CaO, 0-11 wt. % MgO, 0.2-1 wt. % Fe2O3, 0.05 or greater wt. % RE2O3, 0-4 wt. % BaO, 0-4 wt. % SrO, and 0-5.5 wt. % ZnO, wherein the sum of BaO+SrO+ZnO is greater than about 2 wt. %. In another embodiment, a glass composition suitable for fiber forming comprises 51-70 wt. % SiO2, 12.5-22 wt. % Al2O3, 0-20 wt. % CaO, 0-11 wt. % MgO, 0.2-1 wt. % Fe2O3, 0.05 or greater wt. % RE2O3, and from greater than 0 to 2.5 wt. % Cu2O. In another embodiment, a glass composition suitable for fiber forming comprises 51-70 wt. % SiO2, 12.5-22 wt. % Al2O3, 0-20 wt. % CaO, 0-12.5 wt. % MgO, 0.2-1 wt. % Fe2O3, 0.05 or greater wt. % RE2O3, and at least one additional feature selected from the group consisting of: La2O3 is present in an amount greater than about 2 weight percent, CaO is present in an amount less than about 2 weight percent, a MgO/CaO ratio less than about 1, and a SiO2/Al2O3 ratio greater than about 4. 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.