As global momentum and investment for accelerating maternal and child survival grows, monitoring of progress at the global and country level has become even more needed. Millennium Development Goal 4 (MDG 4) calls for a two-thirds reduction in the mortality rate among children under the age of 5 years between 1990 and 2015. Generating accurate estimates of under-5 mortality poses a considerable challenge because of the limited data available for many developing countries. In response, experts at UNICEF, WHO, the World Bank, the UN Population Division (UNPD), and members of the academic community formed the Inter-agency Group for Child Mortality Estimation (IGME).1 The IGME aims to source and share data on child mortality, to improve and harmonise estimation methods across partners, and to produce consistent estimates on the levels and trends in child mortality worldwide.