Complementarity between multilateral and bilateral aid is essential to ensuring Official Development Assistance (ODA) has impact and is effective. This paper examines whether multilateral outflows and the “multi bi” (or earmarked) aid of Development Assistance Committee (DAC) members are complementary with their bilateral aid along three dimensions: by theme, by geography, and by financing instruments. It concludes positively, but also reveals contrasted visions of the role of multilateral aid across the DAC membership, and some risks stemming from recent shifts in the characteristics of multilateral outflows and multi-bi aid.