Across the tree of life, genetic conflicts between hosts and pathogens have fueled the diversification of intracellular defenses that collectively define innate immunity. While prokaryotic and eukaryotic immunity have long been considered distinct, the recent discoveries of multiple defense systems protecting bacteria against phages have profoundly challenged this paradigm. In particular, some components of eukaryotic innate immunity were shown to have a deep evolutionary origin in bacterial defenses. Our lab investigates how phage-bacteria interactions can illuminate the genetic conflicts between hosts and pathogens across the tree of life.