The last few years have seen a welcome re-emphasis on the need to address the unmet health needs of pregnant women and children worldwide in an integrated manner. Although a number of high profile publications have synthesised the main challenges, scientific evidence and policy recommendations for improving maternal and child health, there are many uncertainties and even disagreements about how maternal, neonatal and child health (MNCH) services and interventions should be scaled up. This paper describes the existence of eight 'tensions' which underlie these uncertainties and disagreements. These are competition between maternal and child health needs for scarce resources; demands for investment across the full continuum of care; balancing the provision of community and facility-based services; bridging the selective-comprehensive divide; using evidence but recognising its limitations; managing both the public and the private; improving both supply and demand; and balancing short-term urgent demands with long-term needs. Based on a review of the literature and the experience of researchers belonging to the UK Department of International Development's research programme consortium on maternal health, this paper discusses the implications of these tensions for MNCH advocates, policy makers and planners, and makes three sets of recommendations. Two key messages are the need for more harmonisation between the MNCH and health systems development agendas and greater recognition of the limitations of universal 'gold standard' evidence in informing policy development and implementation. © 2010 Royal Society of Tropical Medicine and Hygiene.