Pregnancy is a momentous life event experienced by most women that involves biomedical and psychosocial changes that are potentially stressful. High levels of maternal stress in pregnancy contribute to adverse fetal, infant, child, and adult outcomes, including cognitive, emotional, neurodevelopmental, and physical health effects. This article discusses definition, measurement, and effects of stress in pregnancy and describes current research questions such as whether the timing or pattern of prenatal stress accentuates its effects and whether prenatal stress accounts for ethnic disparities in adverse birth outcomes in the United States. We review research on the ways that women cope with prenatal stress and research examining associations of coping with maternal emotional state, health, and birth outcomes. Additionally, we describe important factors that improve women's psychosocial adaptation to pregnancy, their health, and their birth outcomes, specifically trait optimism, social support, and physical activity, and we emphasize interventions that utilize these factors.