Quantum Coherent Electron Transport (QCET) devices are potentially most fast semiconductor devices that can be based on band-edge engineering. Among their closest relatives they have Resonant-Tunneling (RT) diodes and mid and far infrared Quantum Cascade (QC) lasers. In those devices, however, generally Phonon Assisted Electron Transport takes place rather than QCET. The QCET will occur when the electronic lifetime in each active region of a device is determined mostly by intra or inter-band tunneling rather than scattering processes. Employing QCET can lead to a breakthrough in many characteristics of such devices, making possible, for example, very high (close to 100%) quantum efficiencies per active stage of a QCET laser and striking increase in working frequencies of RTs. These advantages of QCET become even more vital as far as pushing QC laser down and RT diodes up into the THz frequency band are concerned. In this paper, we show that the entire THz band can be covered by QCET active devices, which structure should be based on band-edge and wave function engineering.