This chapter examines the role of glucocorticoids as signals in the developmental programming of the placenta, with particular emphasis on the specific actions of these steroids on placental structure and function. The placenta is exposed to glucocorticoids from both the maternal and the fetal circulations and thus receives environmental and maturational signals. The placental supply of nutrients and oxygen to the fetus occurs primarily by diffusion and transporter-mediated transport. In sheep, glucocorticoids affect the gross morphology of the placenta when given either maternally or fetally. Glucocorticoids alter not only the production but also the metabolism of key hormones in the placenta. Glucocorticoid treatment may disturb the balance between pro-oxidant and antioxidant factors in tissues by altering the activity of important antioxidant enzymes. They can also affect the abundance of the transporter molecules required for facilitated diffusion and active transport of key nutrients across the placenta.