The environment of the fetus in the womb is emerging as a key determinant not only of its immediate status but also of the offspring’s long-term well-being. This largely started with reports of striking epidemiological associations between lower, but still normal, birth weight and a marked increase in the incidence of cardiac, metabolic and neuropsychiatric disorders from childhood to senescence. In seeking to explain these observations, collectively referred to as ‘developmental programming,’ a new subfield of biology has emerged. Major discoveries include detailing the etiological roles of maternal factors such as nutrition, inflammatory disease, stress and psychopathology. Key biochemical mediators have been discovered, notably including hormones such as glucocorticoids, which act on both the fetus and the placenta to change the trajectory of growth, tissue maturation and the expression of specific genes in affected cells. Such persisting changes in the transcription of genes may be in part underpinned by epigenetic changes. The mechanisms of these effects are beginning to emerge and offer the prospect of new diagnostics, biomarkers and potential therapeutic targets. This work provides an accessible and cutting-edge view of this rapidly emerging field.