Background: Trials have shown efficacy of rigorous diet and physical activity promotion programs to reduce diabetes incidence and improve glycemic measures in adults at increased risk for type 2 diabetes. Purpose: To evaluate diet and physical activity promotion programs for persons at increased risk for type 2 diabetes, primarily to reduce diabetes risk and decrease body weight and glycemia. Data Sources: MEDLINE, the Cochrane Central Register of Controlled Trials, CAB Abstracts, Global Health, and Ovid Health- STAR from 1991 through 27 February 2015, with no language restriction. Study Selection: 8 researchers screened articles for singlegroup or comparative studies of combined diet and physical activity promotion programs with at least 2 sessions over at least 3 months in participants at increased risk for type 2 diabetes. Data Extraction: 7 researchers extracted data on study design; participant, intervention, and outcome descriptions; and results and assessed study quality. Data Synthesis: 53 studies (30 of diet and physical activity promotion programs vs. usual care, 13 of more intensive vs. less intensive programs, and 13 of single programs) evaluated 66 programs. Compared with usual care, diet and physical activity promotion programs reduced type 2 diabetes incidence (risk ratio [RR], 0.59 [95% CI, 0.52 to 0.66]) (16 studies), decreased body weight (net change,-2.2% [CI,-2.9% to-1.4%]) (24 studies) and fasting blood glucose level (net change, -0.12 mmol/L [-2.2 mg/dL] [CI, -0.20 to -0.05 mmol/L {-3.6 to -0.9 mg/ dL}]) (17 studies), and improved other cardiometabolic risk factors. Evidence for clinical events was limited. More intensive programs were more effective. Limitations: Wide variation in diet and physical activity promotion programs limited identification of features most relevant to effectiveness. Evidence on clinical outcomes and in children was sparse. Conclusion: Combined diet and physical activity promotion programs are effective at decreasing diabetes incidence and improving cardiometabolic risk factors in persons at increased risk. More intensive programs are more effective.