Adventitious presence of GM seeds in non-GM maize production is mainly related to cross pollination between GM fields and neighbouring non-GM fields, GM impurities that may occur in seed lots and admixture due to machinery processes. A large amount of information about on-farm adventitious GM presence in maize production is now available and has been collated at the European level. Predictive gene flow models at the landscape level have been designed and can been used to assess the feasibility of coexistence under various contexts and to identify the coexistence measures that farmers should put into place. Operational decision-support systems, based on these predictive models, are being developed in order to help decision-makers, farmers, and supply chain operators to assess and implement practical coexistence measures