I will provide an overview of our studies of the evolutionary dynamics of transposable elements and their impact on eukaryotic evolution. The emphasis will be on class 2 or DNA transposons in mammalian genomes. Genomic analyses reveal that a vast diversity of DNA transposons exists in mammalian genomes and that large cohorts of elements have been integrated in a lineage-specific fashion, generating extensive genomic variation among and within the major lineages of placental mammals. The evolutionary dynamics of DNA transposons in mammals is characterized by repeated episodes of horizontal transfer across widely diverged species, a mode of transmission that appears to be facilitated by blood-borne invertebrate parasites. Through several examples, I will illustrate how DNA transposons have been a recurrent source of genetic innovation throughout mammalian evolution, contributing to the shuffling of pre-existing genes and to the emergence of new genes and concomitantly to the assembly of lineage-specific regulatory circuits.