Polymorphism has been an active area of research for decades. To gain more insight into this field, we have developed an evaporation-based crystallization platform [Talreja et al. (2005) J. Appl. Crystallogr. 38: 988-995; He et al. (2006) Cryst. Growth & Des. in press] to systematically study the effects of the rate of supersaturation on crystallization kinetics and polymorphism. Here we report the selective growth of g glycine crystals via concentrating microdroplets of aqueous glycine solutions through slow evaporation of water using the abovementioned platform. In prior studies, g glycine crystals could only be obtained from non-neutral pH solutions, by applying electromagnetic fields, or in the presence of impurities that suppress the formation of the kinetically favored a glycine polymorph. Pure g glycine crystals form below a certain rate of evaporation (i.e. below a certain rate of supersaturation). Below this rate the crystallizing solution stays close to equilibrium throughout the evaporating process allowing the system to sample the lowest free energy state during the formation of nuclei. These results nicely display the interplay of kinetic and thermodynamic effects on selective crystallization of different polymorphs. Polymorphic analysis was performed by examination of all samples as randomized polycrystalline particles. The resulting multi-frame diffraction patterns were combined to generate a single powder X-ray diffraction (PXRD) spectrum of each sample. Compared to traditional powder diffraction methods, the quantitative polymorphic analysis procedure reported here eliminates the need to mechanically grind crystalline material, thereby avoiding the potential for undesired polymorphic transformations prior to data collection.