CGIAR Challenge Programs were the early precursors of our Research Programs. First conceived in the late 1990s they built complementarities, synergies, and collective action among Research Centers. The Challenge Programs introduced a new model for collaborative research. This new model sometimes takes a participatory, farming systems approach to developing and disseminating technology and breaks through the divisions typical of research-extension-farmer hierarchies. All those involved, together with manufacturers and suppliers, work in teams. Everyone gains by sharing knowledge and technological innovation is more dynamic. All Challenge Programs are being integrated and mainstreamed into appropriate CGIAR Research Programs.