The importance of the Quantum Hall effect in metrological standards is well established, but its implementation in many situations is hindered by its requirements of a strong magnetic field. Recently, a new material class, magnetically doped topological insulators, has been shown to exhibit an effect, dubbed Quantum Anomalous Hall Effect, with completely novel physical origins and providing a quantized Hall plateau without needing magnetic field. This paper examines the nature of this effect, with particular focus on the fact that an axionic action term must be added to the electrodynamic considerations to properly describe the action in three-dimensional topological insulators.