The compositional dependence of the dissolution rates of ternary alkali-alkaline earth borate glasses in water were characterized. These glasses dissolve congruently and the dissolution kinetics were linear, following the contracting volume model for spherical particles. The dissolution rates were dependent on the glass structure, with slower rates associated with glasses with greater fractions of four-coordinated borate sites in their network structures, as determined by nuclear magnetic resonance spectroscopy. For glasses with a fixed alkaline earth identity, the dissolution rates increased in the order Li < Na < K. For glasses with a constant alkali identity, the dissolution rates increased in the order Ca < Sr ≈ Mg. The effects of composition on dissolution rates are discussed in terms of the reactions between water and different borate and metal-oxide sites in the glass structure.