This chapter discusses the use of synthetic onlays and inlays implanted in the cornea to treat various conditions, specifically refractive errors. As the cornea is the primary refractive component of the eye and surgically the most accessible, providing surgical refractive correction at the corneal plane is a logical approach. A corneal onlay is intended to be placed at the very anterior aspect of the corneal stroma, often anterior to S. W. Bowman’s membrane after removal of the epithelium, and the epithelium is either replaced or regrows over the surface of the onlay. Shape-changing implants generally have a similar index of refraction as the cornea and primarily act to change the surface curvature of the cornea. Placing an inlay within the corneal stroma or an onlay within the more superficial layers of the cornea requires careful consideration of the cornea’s physiological response to injury or the presence of a foreign body.