This paper explores adolescent pregnancies, child marriages and early unions in Southeast Asia and the Pacific by investigating their prevalence, trends, drivers, patterns and typologies. It highlights that whilst there is considerable heterogeneity across the region, in many settings, progress to address these issues has stalled. The paper proposes the differing patterns of adolescent pregnancy, child marriage and early union observed require different intervention strategies. In doing so, it lays the foundation for the second paper in the series Beyond Marriage and Motherhood: Tailoring Programme Interventions for Southeast Asia and the Pacific.