Eight amorphous, thermoplastic aromatic poly(ether)s and poly(ether ketone)s, some containing fluorine, were investigated by dielectric relaxation spectroscopy over the frequency range 20-10(5) Hz and the temperature range -130-300 degrees C. For the polymers containing perfluorophenylene units, three relation processes were observed; one corresponding to the glass transition (or-relaxation), and a further two sub-T-g secondary process (beta- and gamma-processes). For polymers without perfluorophenylene units, a beta-process was not detected. The sub-T-g transitions followed Arrhenius behaviour and were sensitive to polymer structure and chain flexibility. The sub-ambient relaxation exhibited a strong dependence on absorbed moisture. The polymers containing perfluorophenylene units showed a significant decrease in dielectric permittivity at 100 kHz and this was attributed mainly to a reduced electronic polarisability. The alpha-relaxation strength of the perfluorinated polymers, which arises from dipolar motions, was also reduced.