The microstructure and dynamics of semicrystalline, melt-miscible poly(ethylene oxide)/poly(vinyl acetate) (PEO/PVAc) blends were investigated using small-angle X-ray scattering (SAXS) and broadband dielectric relaxation spectroscopy, respectively. PEO/PVAc blends with selected compositions were crystallized, and SAXS Was used to determine the location of the noncrystallizable PVAc in the structure. Values of the microstructural parameters indicate that little, if any, PVAc is incorporated into interlamellar regions under these crystallization conditions, but PVAc diffuses to interfibrillar regions during the crystallization process. For crystalline blends, a dielectric relaxation appears in the same location as the neat PEO alpha-process, indicating the presence of relatively mobile amorphous segments consisting almost entirely of PEO, in blends with compositions having as much as 50% PVAc. Considering the findings from the SAXS experiments, we attribute alpha(PEO) in the blends to the segmental process of the mobile portion of the interlamellar PEO segments. The shape of an observed higher temperature dielectric relaxation, particularly for blends with 30% and 50% PVAc content, suggests that it consists of multiple overlapping processes. The evidence suggests that these are a Maxwell-Wagner-Sillars (MWS) interfacial polarization process (similar to the one observed for neat PEO), a slow segmental process associated with amorphous interfibrillar regions, and possibly a second MWS relaxation.