Hydrolytically stable phosphorus-containing monomers, such as 4,4’-bis(fluorophenyl)methylphosphine oxide (BFPMPO), 4,4’-bis(hydroxyphenyl)methylphosphine oxide (BOHPMPO), and 4,4-bis(hydroxyphenyl)phenylphosphine oxide (BOHPPO), were synthesized and used in nucleophilic aromatic substitution polycondensation to prepare poly(arylene ether phosphine oxide) engineering thermoplastics. The synthesis and characterization of these novel polymers are described. It was determined that by incorporating the phosphine oxide moiety into the polymer backbone, certain properties of the resulting poly(arylene ether) were substantially improved, such as an increase in T-g, thermal stability in air, modulus, and char yield compared with control poly(arylene ether sulfone)s. The high char yields obtained for these polymers in air along with observed intumescence indicates that these materials have improved fire resistance. Preliminary cone calorimetry measurements support this conclusion.