The first months after becoming a new parent are a unique and important period in human development. Despite substantial research on the many social and biological changes that occur during the first months of parenthood, little is known about changes in mothers’ attachment. The present study examines developmental stability and change in first-time mothers’ attachment style across the first 2 years of motherhood. At Time 1, 162 economically stressed primiparous mothers (Mage = 23.98 years, SD = 5.18) completed measures of attachment anxiety and avoidance at five time points: when their children were 0, 6, 12, 18, and 24 months of age. Converging results of stability functions and latent growth curve models suggest that attachment styles were generally stable during the first 2 years of motherhood, even in this economically stressed sample. Furthermore, model comparisons revealed that a prototype model better characterized the developmental dynamics of mothers’ attachment style than did a revisionist model, consistent with previous studies of adults and adolescents. This suggests that a relatively enduring prototype underlies mothers’ attachment style and anchors the extent to which mothers experience attachment-related changes following the birth of their first child. Within this overall picture of continuity, however, some mothers did show change over time, and specific factors emerged as moderators of attachment stability, including maternal depressive symptoms and overall psychological distress, as well as sensitive care from their own mothers. Findings shed light on patterns of continuity and change in new parents’ development.