The first 1,000 days, or the period from conception through age 2, is increasingly recognized as a critical period for the development of childhood obesity and its adverse consequences. This issue brief is based on two review papers that examined evidence on risk factors for developing childhood obesity and interventions that could prevent childhood obesity later in life. The evidence is presented on risk factors from conception to delivery, and from birth through age 2. Several risk factors were consistently associated with later childhood overweight: higher maternal pre-pregnancy BMI; maternal excess weight gain during pregnancy; prenatal tobacco exposure; high infant birth weight; and high infant weight gain. The evidence on interventions includes those conducted during pregnancy, those starting at pregnancy and continuing after birth, and those starting after birth but before age 2. Only a small number of effective early-life interventions for childhood obesity were found, and most interventions focused on individual or family-level behavior changes. Interventions focusing on multiple risk factors and delivered across a variety of settings may help reduce childhood obesity risk.