Prokaryotes have evolved a multitude of immune systems to defend themselves from virus predation including known gems such as CRISPR-Cas and Restriction enzymes. Recent years have seen a dramatic increase in known virus defense mechanisms in prokaryotes. In my talk I will give an overview of antiviral defense in bacteria, and will reveal a number of new antiviral defense mechanisms related innate immune pathways in Eukaryotes. I will highlight CRISPR-controlled proteases in antiviral defense, and I will furthermore discuss the relevance of virus defense for the development of virus-based antimicrobial strategies (phage therapy). Finally, I will present phage countermeasure strategies able to subvert host immunity.