Reactive oxygen species (ROS) are ubiquitous, short-lived, and small diffusible molecules that are generated as natural by-products of aerobic respiration and metabolism. The control of ROS production by antioxidants is a key element for aerobic life. Adverse prenatal developmental outcome is one of the major concerns in reproductive medicine and health. The high metabolic rate during pregnancy results in great consumption of oxygen and energy substrates, resulting in greater in utero exposure of the developing embryo/fetus to high levels of ROS. The protection of the developing organism in utero from ROS-induced oxidative damage is ensured by antioxidant systems to cope with locally produced ROS and prevent their overproduction and propagation to highly reactive and toxic ROS. Maternal exposure to multiple environmental factors contributes to adverse prenatal developmental outcomes, at least in part, via ROS generation. ROS-induced oxidative damage is considered to be a promoter of several prenatal developmental disorders, including defective embryogenesis, embryopathies, embryonic mortality, spontaneous abortion, recurrent pregnancy loss, fetal growth restriction, intrauterine fetal death, preterm delivery, and low birth weight. In this chapter, the roles of ROS and antioxidant systems in prenatal developmental outcomes are reviewed. The links between environmental factors, oxidative stress, and the associated adverse prenatal developmental outcomes are highlighted.