The arms race between bacteria and phages led to the development of sophisticated anti-phage defense systems, collectively called the “immune system” of bacteria. A flurry of recent discoveries showed that the microbial pan-genome contains over 300 defense systems, many of which are still unexplored. The talk will present progress in understanding the mechanisms of action of new bacterial defense systems, will highlight cases in which bacterial defense from phage gave rise to key components in the eukaryotic innate immune system, and will demonstrate how phages evolved to overcome bacterial immunity.