Over the past decade a variety of physical phenomena have emerged which are exercising profound constraints on the speed of devices whose primary transient is electronic in origin. For example, the broad high frequency extrapolations of high speed arising from velocity overshoot were found to be limited by the effects of space charge and the imposition of fields that take a finite time to reach their specified level. Much of the latter problem may be minimized through optical processes, but in its place rests the constraints of electron-hole interaction and other processes that may require quantum coherence for implementation. In the case of electron-hole interaction it has been found that it provides an important channel through which electron energy is transferred to the lattice, and that the electron cooling rates at high hole concentrations are higher when the electron-hole interaction is included, than when it is ignored. At low hole concentrations the reverse is true. The effect of electron-hole interaction also influences velocity overshoot. In the case of quantum coherence, of interest is the effect, e.g., of temporal scatterers (phonons) on the time dependent wave functions and modifications of interference effects. The influence of space charge on transient velocity overshoot, the effects of electron-hole interaction on the relaxation of an electron-hole plasma, and the effects of time dependent and time independent scattering on quantum interference will be discussed.