Both the developing fetus and the placenta require fatty acids for the synthesis of complex lipids necessary for the biogenesis of plasma membranes, intracellular membranes, and organelles; triacylglycerol stores; and secreted products such as lipoproteins, bile, and pulmonary surfactant. Although fetal tissues can readily synthesize fatty acids, considerable evidence exists in nonruminants that as much as 50% of the fatty acid requirements of the fetus are maternally derived. The placenta may be even more dependent than the fetus on the maternal contribution because the placenta synthesizes fatty acids poorly. The major sources of fatty acid provided to the fetus and placenta have not been identified with certainty. Maternal free fatty acids readily cross the placenta and the fatty acid moieties of maternal serum lipoproteins may also be transferred. The mechanism of transport of maternal free fatty acids and lipoprotein-carried lipid has not been investigated on a molecular level. Future studies with cultured trophoblasts should be useful in providing answers to many questions concerning placental lipid metabolism and the role of the placenta in transporting lipid to the fetus.