Polyphase decision-feedback sequence estimation (PDFSE) is a generalised sequence estimation algorithm that provides a tradeoff between complexity and performance in digital communications over intersymbol interference (ISI) channels. In PDFSE a sequence is divided into several polyphase components and each component estimated separately. Interphase interference (IPI) is eliminated through decision-feedback. The performance/complexity ratio of the PDFSE is superior to that of reduced-state sequence estimation (RSSE) for some channels in which the energy of the channel impulse response (CIR) is not concentrated in the front part.