Hybridisation and introgression from crops to wild relatives is a key issue in risk assessment. These dynamics between wheat and tetraploid Aegilops L. species were investigated by experiments in natural conditions or in the greenhouse, and by genetic analyses. DNA fragments from different wheat genome areas were tracked along introgression lines with Aegilops cylindrica Host, demonstrating that transgene flow might occur significantly in a scenario of wide cultivation of GM wheat. Insertion of transgenes in unshared genomes between the species would not necessarily prevent functional gene escape into wild grasses. In order to describe crop-weed dynamics in agroecosystems and to quantify inheritance of transgenes, we assessed fertility of the hybrid progeny, pollination distances, molecular and chromosome constitution, and transgene expression. The study then assesses population genetic structure of wild Ae. cylindrica over two continents, revealing a low genetic diversity within the species. The last chapter describes early generation introgression between wheat and Aegilops geniculata Roth, the most widespread and frequent Aegilops species in the Mediterranean area.