Almost half of pregnant women in the US begin their pregnancies obese or overweight and more than half experience excessive gestational weight gain. These women are at increased risk for complications such as gestational diabetes, gestational hypertension, and pre-eclampsia. Obese women require more operative interventions at delivery and suffer more postpartum infections. Growing evidence suggests that a mother's weight at pregnancy onset, and excessive weight during pregnancy, are associated with an increased risk that her child will become obese and face obesity-related health issues. We have successfully helped women avoid excessive weight gain during pregnancy with a program started in the first trimester. However, organogenesis and metabolic programming begin early in the first trimester, well before the first prenatal visit. Therefore, waiting to addess mothers' weight, physical activity, and diet is not optimal. We propose to conduct a randomized clinical trial to evaluate a comprehensive pre-conception program to help obese and overweight women improve diet and physical activity habits and lose weight prior to becoming pregnant, and to not gain excessive weight during pregnancy. Because women considering pregnancy have many demands on their time, we modeled our intervention after successful remote, yet frequent contact interventions.1-3 We will use face-to-face counseling with a personal health coach followed by 24 months of frequent phone counseling with the same coach and access to a supportive website. The study will be conducted in an integrated health plan, Kaiser Permanente Northwest (KPNW). A random sample of women in KPNW have expressed high interest in a preconception lifestyle program. We will use KPNW's extensive electronic medical records to identify women with a high likelihood of pregnancy, and invite them to participate. We will implement a randomized clinical trial to test a personalized weight management intervention in comparison to usual care control for women with a BMI e 28 who are planning a pregnancy in the next two years. We believe that by improving mothers' weights, diet quality, and activity levels, the intervention will lead to offspring with lower birth weight (closer to national norms) compared to birth weights above norms in offspring of control mothers. We believe the intervention, delivered via telephone and website, will be highly acceptable to reproductive aged women. If we demonstrate that helping women start pregnancy at a healthier weight improves their own health and that of their children, this program could be quickly implemented in a variety of settings, and could have enormous potential to reduce obesity and improve public health for generations to come.