The ferroelectric members of the KDP-family exhibit piezoelectricity in both the paraelectric and ferroelectric phases, and pyroelectricity in the ferroelectric phase. The piezoelectric effect has been studied extensively, both fundamentally and for applications. Its anomalous behavior in the vicinity of the Curie point has been shown to be a direct consequence of the dielectric anomaly. The much-less examined pyroelectric effect has been used for determining spontaneous polarization and studying low-lying optic modes. Most of the piezoelectric data on the KDP-family available in the literature are discussed in this paper.