A database containing solubilities originally published in the International Union for Pure and Applied Chemistry (IUPAC)-NIST Solubility Data Series has been made available online. The data were originally published in eleven volumes of the Solubility Data Series. Mutual solubilities and liquid-liquid equilibria of binary, ternary and quaternary systems are presented. Typical solvents and solutes include water, sea water, heavy water, inorganic compounds and a variety of organic compounds such as hydrocarbons, halogenated hydrocarbons, alcohols, acids, esters, and nitrogen compounds. For many systems, sufficient data were available to allow critical evaluation. Data are expressed as mass and mole fractions as well as the originally reported units.