Terahertz quantum-well photodetectors (THz QWPs) are photon-type detectors working in terahertz regime. Recent progress in the development of terahertz QWPs is reviewed in the following aspects. First, by considering the many-particle effects, the response peak frequency and the band structure of terahertz QWPs are calculated and optimized accurately; the electron transport behavior is explored within the self-consistent emissioncapture model. Second, three types of light couplers for terahertz QWPs are introduced. At resonant frequencies, the polarization of the light field is effectively tuned by the light couplers to fulfill the selection rule for intersubband transitions. The electric field intensities in the active multi-quantum-well (MQW) absorption region of terahertz QWPs are also enhanced. Therefore, the sensitivity of terahertz QWPs is improved. Third, the anomalous response peak at the longitudinal optical (LO) phonon frequency of GaAs is found in terahertz QWPs. Such response peak originates from the field enhancement in the MQW absorption layer mediated by LO phonons.