Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during manufacturing, shipping, storage, and end-use of PLA products. Crystallinity in PLA was measured with Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD). Moisture sorption isotherms in. PLA films were measured with Quartz Crystal Microbalance (QCM) and Dynamic Vapor Sorption (DVS) experiments with samples of varying crystallinity. A surprising result is that crystalline and amorphous PLA films exhibit nearly identical sorption isotherms, within the accuracy of the experiments. The effect of hydrophobicity of PLA end groups on degradation was evaluated by synthesizing PLA with hydrophobic and hydrophilic end groups.