The prevalence of type 2 diabetes is rising among African American and Latino women of childbearing age, with severe consequences for individuals, families and communities. Diet and exercise behaviors, excessive pregnancy weight gain and postpartum weight retention may lead to the development of longer-term obesity that contributes to this trend. The prenatal-postpartum period offers a unique opportunity for interventions that may reduce these risks. The overall aim of this community-based randomized controlled clinical trial is to demonstrate the effectiveness of a healthy lifestyle intervention tailored to the needs of pregnant and postpartum African American and Latino women in Detroit, Michigan and designed to reduce behavioral and clinical risk factors for type 2 diabetes. Two hypotheses (specific aims 1 and 2) will be tested: Compared to the control intervention, healthy lifestyle intervention participants will have 1) improved levels of protective behaviors (increased daily level of physical activity and improved daily dietary composition) that reduce the risk of type 2 diabetes; and 2) improved their status on clinical measures of risk for type 2 diabetes (anthropometric and metabolic status). Specific aim 3 addresses whether theory-based variables, including changes in attitudes, behavioral and control beliefs, perceived social support and behavioral intention change from baseline, and whether these changes influence behavioral outcomes. Specific aim 4 will identify aspects of project planning and implementation that contribute. to achievement of behavioral and clinical outcomes. The study will be conducted by an existing partnership between university and community organizations that has a successful record of community-based participatory epidemiological and intervention research. The healthy lifestyle intervention draws from the theories of planned behavior and social support and takes into account specific social, cultural, economic and physical environmental challenges faced by low-income women in Detroit. It addresses the rapidly changing context of pregnancy and the postpartum period, which bring additional challenges but also opportunities for adoption and maintenance of healthy behaviors. The target population will be 400 Latino and African American women who will be recruited in prenatal care settings during their first trimester of pregnancy. After a qualifying period designed to reduce later attrition, 320 will be randomized into either a healthy lifestyle intervention or a control intervention group. The healthy lifestyle intervention will include a 17-session curriculum that integrates pregnancy, childbirth and postpartum preparation, social support from a Women's Health Advocate (WHA) and group social support activities. The control intervention group will receive a 4-session curriculum that integrates pregnancy, childbirth and postpartum preparation. Measures will be collected at 10-14 weeks, -26 weeks and -36 weeks of gestation and -6 weeks postpartum.