To counteract CRISPR–Cas defences, phages have evolved anti-CRISPR (Acr) strategies that can inhibit prokaryotic adaptive immunity. Acrs are frequently encoded in an operon with a conserved anti-CRISPR-associated (aca) gene. Aca proteins are DNA binding proteins and regulate their corresponding acr–aca loci. We have demonstrated that representatives of most classes of Aca proteins function as repressors. The purpose and molecular basis of this Acr regulation is poorly understood. I will present our work on anti-CRISPR regulation, including unexpected findings into how this regulation contributes to the control of anti-CRISPR activity. Finally, I will describe our discovery and characterisation of a new mechanistic group of anti-CRISPRs encoded by phages and other mobile genetic elements.