Ab initio configuration interaction calculations have been carried out for the lower electronic states of the glycine zwitterion in both the gas phase and in dilute aqueous solution. The solution calculations employ a fractional charge model for the water molecules. The calculated gas phase and solution spectra differ sharply. While excited electronic states of marked Rydberg character are more strongly affected than are valence states, all transitions are shifted to higher energy in solution. We find good agreement with experimentally observed optical absorption spectrum of the glycine zwitterion in thin films. © 1986, American Chemical Society. All rights reserved.