Although the idea of preventing type 2 diabetes has been articulated since the discovery of insulin, only in the past decade have clinical trials demonstrated that diabetes can be prevented or delayed. These trials found lifestyle intervention reduces diabetes incidence by over 50% and is more efficacious than metformin. Evidence from prevention trials comes from persons with "pre-diabetes" in which blood glucose levels are elevated but not yet in the diabetes range. In normoglycemic persons, lifestyle or drug intervention has little impact on diabetes incidence. Prevention programs are often conducted outside the clinical sector where participants' glycemic status is usually unknown; these programs may include many normoglycemic participants, which greatly reduces cost-effectiveness. An economically sustainable system for diabetes prevention will require effective partnerships among the clinical sector, community-based lifestyle programs, and third-party payers to ensure that limited resources for diabetes prevention are focused on persons at high risk of diabetes.