The derivation of Hildebrand's solubility parameter and the inter-molecular forces that influence solubility are discussed. Three of these forces were incorporated into a model which consisted of solubility parameter, hydrogen bonding, and dipole moments, and the resulting three-dimensional plot used to predict the solubility of cellulosic polymers in organic solvents with better accuracy than before. Values for hydrogen bonding were assigned on the basis of Gordy's spectroscopic measurements and the value of a unit of hydrogen bonding strength defined. The polymer-solvent model gave a better understanding of the relationships that exist between solvents and between polymers and solvents. For the first time a graphic illustration of dilution ratio was possible. -- AATA