Model polyurethane ionomer solution studies revealed that the critical parameters determining the solution behavior of ionomers are solvent polarity, solvent-backbone interactions, and ionic content of the ionomer. The three parameters are used to develop a novel ionomer solution diagram which provides a framework for discussion of ionomer solution behavior. The dissolution process of ionomers in low-polarity solvents is analyzed, and two different mechanisms-dissociation and fragmentation-are identified.