This article is intended to help clinicians better understand the ever-expanding body of research on whether psychosocial stress (both acute and chronic) is linked to 2 major adverse pregnancy outcomes: preterm birth and low birth weight. We summarize the existing literature and then review assessment tools commonly used to diagnose various types of psychosocial stress, with attention to how and when assessments should be made. After discussing the physiologic mechanisms hypothesized to underlie these relationships, we examine the range of existing interventions aimed at reducing psychosocial stress and review their efficacy at improving birth outcomes. Future directions for prevention of adverse pregnancy outcomes are discussed and suggest that an entirely new approach may be necessary.