Why do informal, plurilateral summit institutions such as the Group of Eight (G8) major market democracies succeed in advancing costly public health priorities such as maternal, newborn, and child health (MNCH), even when the formal, multilateral United Nations (UN) system fails to meet such goals, when G8 governments afflicted by recession, deficit, and debt seek to cut expenditures, and when the private sector is largely uninvolved, despite the growing popularity of public-private partnerships to meet global health and related nutrition, food, and agriculture needs? Guided by the concert-equality model of G8 governance, this case study of the G8's 2010 Muskoka Initiative on MNCH traces the process through which that initiative was planned within Canada, internationally prepared through negotiations with Canada's G8 partners, produced at Muskoka by the leaders in June, multiplied in its results by the UN summit in September, and reinforced by the new accountability mechanism put in place. It finds that the Muskoka summit succeeded in mobilizing major money and momentum for MNCH. This was due to the initiative and influence of children-focused nongovernmental organizations (NGOs), working with committed individuals and agencies within the host Canadian government, as well as supportive public opinion and the help of those in the UN responsible for realizing its Millennium Development Goals. Also relevant were the democratic like-mindedness of G8 leaders and their African partners, the deference of G8 members to the host's priority, and the need of the G8 to demonstrate its relevance through a division of labor between it and the new Group of Twenty summit. This study shows that G8 summits can succeed in advancing key global health issues without a global shock on the same subject to galvanize agreement and action. It suggests that, when committed, focused NGOs and government officials will lead and the private sector will follow, but that there will be a lag in the implementation needed to obtain the intended results. The need to improve the accompanying accountability mechanisms to improve implementation, thus, remains.