Three papers in this issue of Molecular Cell report on the structure and functional activity of type III CRISPR-Cas effector complexes, revealing novel and conserved features of the ribonucleoprotein particles that underlie prokaryotic genome defense. The new structures suggest that type I and type III complexes follow the same architectural principles and are most likely descendants of a common ancestor, the differences in RNA and protein sequences and structure of individual components notwithstanding.