Among vertebrates, most of the largest genomes are found within the salamanders, a clade of amphibians that includes 600+ recognized species. Salamander genome sizes range from ~14 Gb to ~120 Gb; these values are larger than all bird, mammal, reptile, and frog genomes, as well as most fish genomes. My lab is working to understand the evolutionary processes underlying extreme genome gigantism in the salamander clade. We have shown that salamanders lose DNA more slowly from their genomes than do other vertebrates, both through small (i.e. a few bp) and large (i.e. a few kb) deletions. We have also shown that salamander genomes reflect high levels of transposable elements, but that the relative abundance of different kinds of transposable elements is different in salamanders than in other vertebrates. Within salamanders, we show that life history is a predictor of genome size. In this seminar, I will discuss our ongoing analyses aimed at understanding the evolutionary forces shaping genome size at the vertebrate extremes.