Given the characterisation and evaluation of the gene flow from oilseed rape done by INRA, CNRS and Cetiom, the present paper aims to investigate the possible agro-environmental impacts of gene flow from herbicide-tolerant genetically-modified (GM) oilseed rape (seed loss outside and inside the field, pollen dispersal, interspecific hybridization). We identified two main impacts of the release of such varieties in French agricultural systems: the possible questioning of GM content norms for the harvest of non-GM rape fields, and of the long-term effectiveness of such weed control strategies through the development of tolerant weeds (oilseed rape and hybrids). This text is an extract from a report that summarises French research on gene flow carried out by Cetiom towards the end of the two-year French moratorium on genetically-modified oilseed rape and sugar beet.