Laser retinal photocoagulation represents the primary therapy for the potentially blinding manifestations of diabetic retinopathy. Advances in laser therapy for diabetic eye disease have arisen from the convergence of laser technology and clinical ophthalmology. In this review, the basis of laser therapy in diabetic retinopathy is discussed. Included are the clinical characteristics, classification, and pathogenetic mechanisms of diabetic retinopathy. The principles of laser technology, variety of lasers currently available for therapy, and mechanisms of laser actions on retinal target tissues are introduced. The milestone clinical trials establishing the efficacy of laser therapy and the parameters for its clinical application in diabetic retinopathy are outlined.