Several parallel-form adaptive IIR (infinite impulse response) filters are presented, including a frequency-domain implementation based on the discrete Fourier transform and a recursive frequency-sampling structure. The performance of the frequency-domain adaptive IIR filter is investigated in a system identification application, which includes an analysis of its modeling capabilities and a discussion of the mean-square-error performance surface. Computer simulation results are presented to illustrate the robust convergence properties of the adaptive algorithm and to demonstrate the stability of the filter.< >