Range expansions and contractions exaggerate the reshuffling of the genomes of hybridizing species. The key objective of this project is to experimentally test the theoretical prediction that, under hybrid zone movement, genes derived from a displaced species are left behind in the genome of an invading species, leaving a ‘genomic footprint’. I fill an empirical void by, for the first time, testing this critical hypothesis in the wild, using genome-scale data. I have established a study system (the newt genus Triturus) that is particularly appropriate because it shows strong evidence in support of hybrid zone movement over considerable time and distance. Human activities have intensified hybridization and I work together with conservationists and legislators to tackle the insidious conservation problem of genetic pollution by exotic species.