Europe is adopting measures to ensure the coexistence of conventional, organic and GM-based crop production. Gene flows across field barriers, via seeds and pollen, are inevitable and the aim is to keep the adventitious mixture of GM and non GM products below accepted (negotiated) levels. For achieving this, the long-lasting experience of seed producers and sellers in guaranteeing purity standards proves to be very useful. Coexistence is a purely economical issue, not a biosafety issue : the farmer must be free to choose between the three cropping systems and to comply with the existing regulation on labelling and purity standards with no adverse economical effects. Management scenarios have to be defined minimizing the economic impact and organizing the cooperation between all stakeholders. The measures should be transparent, efficient and cost-effective, without going beyond what is necessary to comply with EU threshold levels for GMO labelling. In order to be realistic and efficient, they need to be adapted to regional peculiarities in land management and agroecological conditions. As a consequence, the Commission decided to rely on Member States to take the appropriate measures in crop and seed productions, while referring to the adopted contamination thresholds (fixed by Regulation (EC) 1829/2003 for food/feed GM products and still debated for seeds). In July 2003, the Commission assisted the Member States by adopting a Recommandation (2003/556/EC) on guidelines for the development of national strategies and best practices. Furthermore, two technical reports were issued, in 2003 and 2006, by the European Commission Joint Research Center (JRC), the Institute for Prospective Technological Studies (IPTS) and the European Science and Technology observatory (ESTO) (http://ftp.jrc.es/eur22102en.pdf), for building technical scenarios and tackling their economic outputs.