This chapter discusses corneal collagen cross-linking in Keratoconus. Corneal collagen cross-linking is performed by using UVA at 370 nm and the photosensitizer riboflavin, stiffening the collagen matrix of the cornea. Cross-linking treatment is the first and only therapeutic option that has changed the natural course of keratoconus by stopping progression. Corneal collagen cross-linking treatment is reserved for progressive keratoconus. Contraindications to corneal cross-linking in keratoconus are presented. The surgical procedure is described. Postoperatively cycloplegic, antibiotic, anti-inflammatory, and artificial tear drops as well as an oral analgesic are prescribed. Clinical results are described. Cross-linking has also been effective following inferior-segment intacs implantation. The addition of collagen cross-linking to the intacs procedure resulted in greater reduction in cylinder, steep and average keratometry and lower-upper ratio in corneal topography than intacs insertion alone. Risks and effects are explained.