While the role of technical change in agriculture is seen differently by protagonists of different theories of development, the processes of technology generation and uptake are widely seen as progressive. In this vein, agricultural technology assessment is seen as contributing to research policy and management and also to the formulation, monitoring and evaluation of broader rural development policies and programs. A need for both farm-level and aggregate-level assessments is identified, and methods applied at each level are reviewed. At the farm level, some insights are provided by the farming systems research approach leading to recognition of a changed role for economists in farm-level impact assessment. At the aggregate level, the problems of tracing out all the important consequences of a technical innovation can be severe. Analysts will generally need to account for general equilibrium effects, distorted prices and welfare considerations, as well as the dynamic interaction between technology and institutions. In the light of the discussion, an agenda of unfinished business for agricultural economists is suggested.