This study evaluates the effectiveness of the World Bank Group's support for health, nutrition, and population (HNP) in developing countries from 1997 to 2008 - totaling more than $17 billion - and distills lessons for greater impact in the future. It finds that the Bank Group now funds a smaller share of global support for HNP than a decade ago, but its support remains substantial and adds considerable value. About two-thirds of the Bank's HNP support has had satisfactory outcomes, often in difficult environments. But in a number of country settings, particularly in Africa, it has not performed well, in part due to high complexity and weak capacity. Only half of HNP support had a pro-poor focus, while support to reduce high fertility and promote family planning has dwindled. The evaluation highlights the contribution of investments in water supply, sanitation, and hygiene to improving the health of the poor and the lessons from support for sector-wide approaches, communicable disease control, and health reform. Moving forward, the World Bank needs to improve the performance of its HNP support and the Bank and IFC need to take actions to ensure their support reaches the poor and contributes greater social benefits, respectively.