Despite the well-established importance of prenatal experiences for offspring health throughout the lifespan, our understanding of prenatal influences on psychological outcomes faces challenges due to a wide-ranging and somewhat fragmented literature. Here, we introduce the special issue of Developmental Psychology, "Prenatal Influences Across the Life Course: Biobehavioral Mechanisms of Development," which draws together a broad collection of 12 empirical studies and one review article. These studies illustrate the diversity in biobehavioral mechanisms and biopsychosocial processes that help explain the long-term impacts of prenatal experiences on human development. Collectively, these studies help to disentangle sources of influence across different life stages (e.g., prenatal from genetic, preconception, and/or postnatal influences) and fill key gaps in the literature, such as the inclusion of minoritized populations currently underrepresented in research, the role of fathers, and protective mechanisms. The research featured in this special issue underscores both the long reach of prenatal influences on child and adolescent development as well as the challenges in observing specific biological mediators given that prenatal risks are currently operationalized as specific or broad cumulative measures. In an effort to organize this complex literature, we propose a guiding framework for how to conceptualize the continued integration of the prenatal environment into the field of developmental psychology. This framework broadens the prevailing dichotomous view of prenatal mechanisms as cumulative or specific to articulate a dimensional approach focused on adaptation. We anticipate that such an approach may uncover meaningful and observable biobehavioral mechanisms of prenatal influence on offspring development in the future. (PsycInfo Database Record (c) 2024 APA, all rights reserved).