Miscibility and crystallization behavior of blends of poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) were examined. The blends exhibit miscibility in the amorphous state over the entire composition range. Crystallization of PEEK is slower in the blends than in the pure compound. Upon crystallization, PEEK segregates from the miscible amorphous state, causing a shift in the composition of the amorphous phase. PEI is found to be located outside the crystalline lamellae of PEEK. Correspondingly, the crystallinity of PEEK in the crystallized blends does not change largely with composition.