Agricultural systems continuously evolve and are forced to change as a result of a range of global and local driving forces. Agricultural and environmental policies are increasingly designed to contribute to the sustainability of agricultural systems and to enhance contributions of agricultural systems to sustainable development at large. The effectiveness and efficiency of such polices in realizing desired contributions could be greatly enhanced if it were possible to perform ex-ante assessments. The European Commission has recently introduced impact assessment of its policies as an essential step in policy development. This paper presents the design and first prototype of a computerized integrated framework to assess, ex-ante, agricultural and environmental policies across a range of scales, from field-farm to region, EU25 and globe. In this large integrated project 30 research groups work jointly on developing the SEAMLESS Integrated Framework. Key requirements of the framework are that it is open, generic and transparent. This puts stringent requirements on the software backbone of the project and on a modular set-up. The framework is developed in close interaction with the targeted prime users, including the European Commission.