The goal of the corrector is to correct for monochromatic aberrations by flattening the wavefront. It is arguably the most important component in an adaptive optics (AO) system. The majority of AO systems use mirrors that can change their shape or deform, hence the name deformable mirrors. Another type of corrector is a liquid crystal spatial light modulator (LC-SLM). These devices are able to change their refractive index. Correctors of this type are becoming more popular as they are generally of lower cost. A more recent corrector type is a deformable phase plate. These types of devices have begun to be implemented in a small number of AO systems. This chapter begins with the general principle behind how each of these three main types of corrector works and follows with an overview of the most important factors to consider when selecting a corrector. Each type of corrector is then discussed in detail, with their advantages and disadvantages presented. This chapter then concludes with a summary.