The European Initiative for Agricultural Research for Development (EIARD) is concerned with maximizing the contribution of agricultural research to the improvement of the livelihoods of poor people in developing countries. A clear view on means of measuring and enhancing the effectiveness of agricultural research for development [2] is, therefore, of considerable importance to its work. For EIARD, impact assessments and evaluations have four main objectives: (a) to enhance the developmental impact of agricultural research investments for poor people; (b) to provide information on the returns to investments in agricultural research for development; (c) to derive strategic and programmatic lessons for future investments in agricultural research for development; and (d) to provide information for use in public awareness work. These objectives suggest three sets of issues. First, if the main objective of impact assessment and evaluation is to increase the developmental impact of research, it is important to recognise and address the complex social, economic and political dimensions of pro-poor innovation. Thus, impact assessments and evaluations should not be limited to directly measurable impacts; they should seek to capture the complexity and non-linear nature of agricultural innovation and sustainable development. Impact assessments and evaluations should also be integrated as far as possible into research programmes, to facilitate internal learning processes and changes that enhance the probability of impact. Second, the difficulty of attributing impact to specific research investments requires special attention. In agricultural research organizations, exhaustive analysis of specific innovation processes is rarely possible because it is extremely difficult, costly, and time consuming. In most cases, a more feasible goal is to establish plausible links between research investments and development impacts. Third, for impact assessments and evaluations to be useful for decision making, policy design, learning, and public awareness, stakeholder interests and intentions need to be assessed, and appropriate information needs to be prepared for different audiences. It is also important to integrate evaluation lessons with other forms of learning