This chapter provides an introduction to image formation, followed by the effects of aberrations and presents an overall look at adaptive optics (AO) systems with a brief analysis of two wavefront sensors and explores the use of liquid crystals for AO with an overview of what is the state-of-the-art in this arena. Choosing a liquid crystal with low viscosity to increase the temporal rate of the cell response usually leads to an increase of the control voltage. The electric field in the liquid crystal layer becomes inhomogeneous and is determined by anisotropy conditions. Nematic liquid crystals have been used as phase retarders for wavefront shaping for a number of years, for example, see references. The control of a liquid crystal device can be achieved using four different techniques: amplitude control, transient method, pulse method and dual frequency control. For adaptive optics purposes, instead, the use of dual frequency control is to increase the rapidity of a liquid crystal wavefront corrector.