The Millennium Development Goals (MDGs) have become the high-profile framework for world debates around development. What’s less known is the story behind the goals and their origins in the work of the Organisation for Economic Co-operation and Development (OECD) and its Development Assistance Committee (DAC). The MDGs are only one example of how the DAC has helped shape development thinking and practices since the 1960s. As the OECD celebrates its 50th anniversary, this special article reviews five decades of development co-operation and assistance, examines the role played by the OECD and the DAC, and looks at the challenges that lie ahead as the OECD enters its second half-century.