The existence of scintillator nonproportionality has been recognized since the 1950’s, when researchers observed that the light yield was not exactly proportional to the gamma or electron energy. From the beginning it was strongly suspected that the nonproportionality phenomenon was responsible for the discrepancy between the predicted (i.e. photon statistical), and observed, resolution. Early-on researchers suggested that the mechanism of nonproportionality was associated with the dynamics of carriers and excitons in the materials, as well as the nature of the high-energy gamma and electron interactions. Subsequently, extensive surveys of scintillator nonproportionality curves have been conducted using the Compton Coincidence Technique, and more recently by the SLYNCI facility, where more rapid data accumulation is possible. However, a comprehensive fundamental understanding of nonproportionality has proved elusive, owing to the complexity and diversity of the material interactions. Nevertheless a great deal of progress has been achieved in the last few years, and the purpose of this Workshop is to share our thoughts and results as a community, in order to move the enterprise of achieving extremely high resolution in scintillators forward as rapidly as possible. One important goal is to eventually develop a predictive capability for scintillator nonproportionality, which could ultimately serve as the basis for selecting and improving the performance of scintillators.