Corneal collagen crosslinking (CXL) has emerged as a frontline therapy in keratoconus and post-LASIK ectasia. This video lecture series explores the history and current uses of crosslinking, including epithelium-off, transepithelial, and concurrent crosslinking with corneal ring segments. In this segment, Dr. John Kanellopoulous describes the evolution of CXL, patient selection criteria, and the merits and risks of various novel treatment strategies. He also shares practical uses and limitations of preoperative diagnostic imaging and future applications such as CXL combined with topography-guided excimer laser ablation.