The major issues in impact assessment for farmer participatory research (FPR) are analyzed. There are many potential ways in which FPR can have an impact; for example, increasing agricultural productivity, improving the management of natural resources or leading to a wider dissemination of innovations. FPR may also be more effective in reaching specific target groups, and it many reduce research costs and develop community capacity. Impact will be measured by different groups, and for different reasons, according to the circumstances.