Present trends suggest that many of the poorest countries in the world, including many in sub-Saharan Africa, will not meet the health-related Millennium Development Goals [1] (MDGs), especially MDG 4 (reducing under-five mortality) and MDG 5 (reducing maternal mortality) [2]. Even in those countries that are on track to meet health MDGs, striking inequities exist among countries and among socioeconomic groups within them [3], despite effective and cost-effective interventions being available to improve population health, including that of vulnerable groups [4]. Such interventions are delivered through health systems, which consist of "all organisations, people and actions whose primary intent is to promote, restore or maintain health" [5], but, in many settings, interactions between weakened health systems and the sometimes conflicting demands of single-disease intervention programmes are hindering the uptake and implementation of life-saving interventions [6]–[8]. A growing number of governments, international institutions, and funding agencies have therefore recognised the urgent need to coordinate and harmonise investments in health systems strengthening in low- and middle-income countries (LMICs) to provide universal social protection and effective coverage of essential health interventions [9].