The last 2 years has seen a marked increase in the prominence of corneal collagen cross-linking as a treatment strategy for progressive keratoconus. This interest has arisen from a body of laboratory evidence documenting the biomechanical and cellular changes induced by cross-linking. The findings of this research provide a plausible rationale for its use in keratoconus to retard the progression of this common disease. The rapidly growing number of clinical reports suggests, not only a consistent stabilizing effect of cross-linking, but that a variable improvement in corneal shape and visual function may also occur in some patients. However, the marked variation in the clinical course of keratoconus, together with the challenges of accurately evaluating refractive error, visual acuity and even corneal shape in this condition, demands further evidence from randomized controlled clinical trials. The aim of this review is to summarize the theoretical basis and risks of corneal collagen cross-linking, along with the available evidence for its use in keratoconus and other corneal disease states.