Since the 1990s, CIP has employed formal economic ex ante and ex post assessment of research to help guide research resource allocation at the Center. Initial work in the mid-1990s on ex ante priority assessment developed estimates of anticipated impacts for each constraints-based project in the Center's research programmes on potato, sweet potato and natural resource management. These estimates confirmed that the Center's investment in most of these projects was broadly appropriate and contributed to some realignment of projects that appeared to have lower impact potential. Subsequent ex post impact studies revealed that some of the research projects were unlikely to achieve their anticipated impacts, whereas other projects exceeded their projected impacts. A second round of programme-wide ex ante priority assessment was carried out in 2005 as part of the Center's strategic plan. The findings from the ex post impact studies were an important input to the new assessment exercise and contributed substantially to revised estimates of anticipated impacts. This impact assessment went beyond economic surplus measures to model the likely impacts of research on metrics for poverty. The influence of formal priority assessment on Center programmes diminished, however, as increased reliance on restricted funding reduced the Center's flexibility in allocating research resources. © CAB International 2009. All rights reserved.