Oxidative stress induced by hyperglycemia is a key factor in the development and progression of diabetes and its vascular complications. Dietary polyphenols have received enormous attention because their consumption has been associated with lower rates of diabetes and cardiovascular diseases. These compounds are of plant origin, and are abundant in fruit, vegetables, chocolate, and nuts, as well as in beverages such as tea, coffee, wine, and soy milk. They can be divided into at least ten separate classes, four of which are important in the human diet: phenolic acids, flavonoids, stilbenes, and lignans. A number of in vitro and in vivo studies support the effect of polyphenols on glucose metabolism, diabetes risk, and diabetic impairments in the nitric oxide-mediated endothelial progenitor cell mobilization and homing. This chapter intends to review the current knowledge on polyphenols, oxidative stress, and vascular damage in diabetes, focusing on the most important and recent advances and challenges for future research.