The phase behavior, crystallization, and morphology of blends based on poly (ether ether ketone) [PEEK] and bisphenol-A polyarylate [PAr] are described. This system is partially miscible in the melt. Upon quenching to an amorphous glass the system displays two glass transitions corresponding to a nearly pure PEEK phase (T-g1) and a PAr-rich mixed phase (T-g2). The presence of the PAr has a strong retarding influence on the rate of crystallization of PEEK in the blends. Cold crystallization from the amorphous glass occurs in two stages with increasing temperature, corresponding to the mobilization of the PEEK-rich and PAr-rich phases, respectively. At lower cold-crystallization temperatures (below T-g2), the immobile PAr-rich phase constrains crystallization of the PEEK-rich phase, as manifested in both a decreased rate of crystallization and decreased bulk crystallinity. Dynamic relaxation studies of the crystallized blends reveal two glass-rubber relaxations originating from interlamellar amorphous populations in the PEEK-rich and PAr-rich phases. In the PAr-rich phase, there is no evidence of large-scale PAr exclusion to interfibrillar or interspherulitic regions.