Crop-to-wild gene flow has received close attention over the past ten years in connection
with the development and cultivation of transgenic crops. In this paper, we review key
examples of crop/wild sympatry and overlapping flowering phenology, pollen and seed
dispersal, the barriers to hybridisation and introgression, the evolution and fate of
interspecific hybrids, their fitness, and the potential cost of transgenes. We pay
particular attention to ways in which the evolution and divergence between crops
and their wild relatives may interfere with these successive steps. Our review suggests
that crop-to-weed gene flow is highly idiosyncratic and that crop gene dispersion will
certainly be very difficult to preclude totally. Future directions for research should
thus focus on the long-term establishment and effects of transgenes on natural
communities.