For the past 3.7 billion years, Earth has been the setting of perhaps the grandest and still ongoing genomic, evolutionary and ecological experiment: the war between bacteria and their viral parasites. Given the unfathomably large global viral and bacterial reservoirs, the former outnumbering the latter at a ratio of 10:1, it is estimated that viral transductions happen in the order of 2 x 10e16 times per second. A sizeable fraction of these infections leads to prokaryotic death, and the subsequent estimated daily turnover of 15% of Earth’s biomass. However, bacteria have not stood around idly: they have developed weapons of their own to fend against their viral invaders, in the form of immune systems.Over the course of evolutionary history, bacteria have developed multiple lines of defence to fend off infections, in the form of innate and adaptive immune systems. These immune systems, in turn, have been domesticated by researchers to develop novel biotechnological tools. Chapters 2 and 3 of this dissertation detail the repurposing of one of these innate immune systems, the bacterial retron, for precise genome editing in human cells, and its further engineering to enable multiple precise edits on individual genomes across the tree of life. Chapter 4 presents a study of the only known bacterial adaptive immune system, the CRISPR-Cas defence system. There, I attempt to discover novel host factors required for CRISPR adaptation, the process by which bacteria create immune memories of infection, and characterise SspA as a novel transcriptional regulator of the process. Taken together, this dissertation contends that bacterial immune systems are inseparable and cannot be properly understood in isolation of their cellular contexts, and argues for a more systems-biological understanding of their regulation and embeddedness within broader cell metabolism.