Small-angle X-ray scattering (SAXS), optical microscopy and differential scanning calorimetry were used to establish relationships between crystallization, microstructure, and equilibrium melting temperature (T-m(0)) for random copolymers of poly(L-lactide-co-meso-lactide). T(m)(0)s derived using the Gibbs-Thomson and data-fitting(23) approaches were found to be in excellent agreement and decreased significantly with increasing meso-lactide concentration. Analysis of these equilibrium melting temperatures using models for copolymer crystallization leads to the conclusion that the meso defects are rejected from the crystalline regions. From analysis of the SAXS data, it was concluded that the copolymers contained significant interfibrillar regions whose concentration increased with higher comonomer content. Spherulitic growth rates were strongly dependent on meso content and were analyzed using the Lauritzen-Hoffman kinetic theory of crystal growth.