Pregnancy is now considered to be an important risk factor for new or persistent obesity among women during the childbearing years. High gestational weight gain is the strongest predictor of maternal overweight or obesity following pregnancy. A growing body of evidence also suggests that both high and low gestational weight gains are independently associated with an increased risk of childhood obesity, suggesting that influences occurring very early in life are contributing to obesity onset. In response to these data, the US Institute of Medicine (IOM) revised gestational weight gain guidelines in 2009 for the first time in nearly two decades. However, less than one third of pregnant women achieve guideline-recommended gains, with the majority gaining above IOM recommended levels. To date, interventions to optimize pregnancy weight gains have had mixed success. In this paper, we summarize the evidence from human and animal studies linking over-nutrition and under-nutrition in pregnancy to maternal and child obesity. In addition, we discuss published trials and ongoing interventions to achieve appropriate gestational weight gain as a strategy for obesity prevention in women and their children.