A formulation for the solubility parameter based on the group-contribution, lattice fluid equation of state was derived. The solubility parameters of pure liquid solvents, polymers, copolymers, and liquid mixtures were calculated and compared against the best available data. This investigation was conducted on pure components and mixtures of alkanes, alkenes, ketones, ethers, acetates, alcohols, chlorinated molecules, and cyclic and aromatic solvents. The capabilities of the model to distinguish between two isomers and to predict the solubility parameter of supercritical fluids and their mixtures were also studied. The predicted values are generally good, although the error increases when hydrogen bonding is present. A primary application of the procedure is for the prediction of the solubility parameters of polymers.