Obesity is now the most common risk factor in pregnancy. Of all pregnant women 10 β 20 % are obese and 1 % are morbidly obese. Both primiparous and multiparous women are increasingly affected by obesity: primiparae because of the rising prevalence of juvenile obesity, multiparae because of inadequate postnatal weight reduction. Pre-conception advice and interventions to minimize maternal and fetal complications of obesity in pregnancy are of vital importance but until now are often sadly inadequate. Obesity associated complications of pregnancy, particularly gestational diabetes, hypertension, pre-eclampsia, and thromboembolism put mother and child at risk. Furthermore, maternal obesity can lead to neonatal macrosomia. Therefore, the Cesarean section rate is high in obese women and vaginal delivery is more often associated with complications of delivery such as shoulder dystocia. Fetal programming during pregnancy is implicated in the development of obesity and the metabolic syndrome in the offspring. This way obesity is passed on from one generation to the next. In order to stop this vicious cycle of obesity, the primary prevention of the obesity epidemic that has taken hold of the Western world has to start in pregnancy. A range of topical issues is discussed in this book including the scientific background behind obesity and pregnancy, complications of pregnancy in the obese, and obstetric care for obese women.