Obesity (Body mass index (BMI) above 30) is one of the major health issues of the 21st century. Over 1.1 billion of the world's population are now classified as obese. In the UK, women are more likely to be obese than men; over 50% of women of reproductive age are overweight or obese. Maternal obesity and the plethora of associated conditions, have a serious impact on the health and development of their offspring. In this review we describe the direct and indirect impact of maternal obesity on the health of the baby. Maternal obesity affects conception, duration and outcome of pregnancy. Offspring are at increased risk of both immediate and long term implications for health. We also briefly review potential mechanisms drawing on data from human and animal studies, and on the outcomes of clinical interventional studies.