Despite extensive attention, obesity rates continue to increase worldwide particularly in children. Accumulating evidence conclusively demonstrates that key aspects of metabolism are ‘programmed’ prior to birth, placing children of obese parents at particularly high risk. Fortunately, our understanding of the underlying cellular events that mediate this developmental programming is rapidly expanding. Obesity in would-be parents alters both egg and sperm as well as every stage of embryo development, through modulation of distinct molecular pathways. Understanding this profound biology provides the basis for new clinical interventions and progressive policy changes.