  In this paper we review some known results on the motion of Bloch Oscillators
in the crystal momentum representation. We emphasize that the acceleration
theorem, as usually stated by most of the authors, is incomplete, but in the
case of pure Bloch states. In fact, the exact version of the acceleration
theorem should contain a phase factor depending on both the time and crystal
momentum variables. As we show this phase factor plays an essential role in
order to understand the motion of Bloch Oscillators in the position variable.
