Many transnational organisations work to support efforts to eliminate maternal and child undernutrition in high-burden countries. Financial, intellectual, and personal linkages bind these organisations loosely together as components of an international nutrition system. In this paper, we argue that such a system should deliver in four functional areas: stewardship, mobilisation of financial resources, direct provision of nutrition services at times of natural disaster or conflict, and human and institutional resource strengthening. We review quantitative and qualitative data from various sources to assess the performance of the system in each of these areas, and find substantial shortcomings. Fragmentation, lack of an evidence base for prioritised action, institutional inertia, and failure to join up with promising developments in parallel sectors are recurrent themes. Many of these weaknesses can be attributed to systemic problems affecting most organisations working in the field; these are analysed using a problem tree approach. We also make recommendations to overcome some of the most important problems, and we propose five priority actions for the development of a new international architecture.