Undernutrition is the single largest contributor to the global burden of disease and can be addressed through a number of highly efficacious interventions. Undernutrition generally has not received commensurate attention in policy agendas at global and national levels, however, and implementing these efficacious interventions at a national scale has proven difficult. This paper reports on the findings from studies in Bangladesh, Bolivia, Guatemala, Peru and Vietnam which sought to identify the challenges in the policy process and ways to overcome them, notably with respect to commitment, agenda setting, policy formulation and implementation. Data were collected through participant observation, documents and interviews. Data collection, analysis and synthesis were guided by published conceptual frameworks for understanding malnutrition, commitment, agenda setting and implementation capacities. The experiences in these countries provide several insights for future efforts: (a) high-level political attention to nutrition can be generated in a number of ways, but the generation of political commitment and system commitment requires sustained efforts from policy entrepreneurs and champions; (b) mid-level actors from ministries and external partners had great difficulty translating political windows of opportunity for nutrition into concrete operational plans, due to capacity constraints, differing professional views of undernutrition and disagreements over interventions, ownership, roles and responsibilities; and (c) the pace and quality of implementation was severely constrained in most cases by weaknesses in human and organizational capacities from national to frontline levels. These findings deepen our understanding of the factors that can influence commitment, agenda setting, policy formulation and implementation. They also confirm and extend upon the growing recognition that the heavy investment to identify efficacious nutrition interventions is unlikely to reduce the burden of undernutrition unless or until these systemic capacity constraints are addressed, with an emphasis initially on strategic and management capacities.