Study reveals new mechanisms by which viral proteins can turn off the CRISPR adaptive immune system of bacteria (Nature 2015, 526, 136-9). The battle for survival between bacteria and the viruses that infect them has led to the evolution of many bacterial systems to defend against these invaders. CRISPR-Cas, one of the most widespread of these systems, is an adaptive system that that specifically targets viral genomes and stores a memory of previous infections. In prior work, a team led by Dr. Alan Davidson and his then graduate student Joe Bondy-Denomy identified the first examples of proteins produced by bacterial viruses that can inhibit CRISPR–Cas systems. In this paper, they elucidated the mechanisms of action of three of these anti-CRISPR proteins, and found that each functions in a distinct manner. This work provides insight into a completely novel group of proteins and increases our understanding of CRISPR-Cas systems, which have recently been developed into powerful tools for human genome editing.