In the paper we present applications of a qualitative multi-attribute modelling method DEX for decision support about the introduction and use of geneticallymodified organisms (GMO) for food and feed. In three 5th and 6th Framework Programme European projects, we have developed a number of models, of which we present three: the »Grignon« model for the assessment of ecological and economic impacts of GMO, ESQI model for the assessment of soil quality, and SMAC model for the assessment of co-existence of conventional and GMO maize. We also mention a decision support system developed within the project Co-Extra. In the second part, we assess the achieved results and describe our lessons learned during the model development.