The CRISPR−Cas protein Cas9 — together with its companion CRISPR RNA (crRNA) and trans-activating crRNA (tracrRNA) — has been developed as a tool for genome engineering, owing to its readily programmable ability to cleave any desired DNA sequence. Now, Zetsche et al. establish a previously uncharacterized CRISPR−Cas protein, Cpf1, as a novel tool with several advantages over Cas9. First, whereas Cas9 generates cleavage products with blunt ends, Cpf1 makes staggered cuts, resulting in a 5′ overhang that improves the precision of DNA insertions. Second, unlike Cas9, Cpf1 cuts at a distal site, which preserves the seed region — essential for target recognition — for future editing. Third, the T-rich protospacer-adjustment motif (PAM; a secondary recognition site) makes Cpf1 better suited to editing AT-rich DNA than Cas9, which has a G-rich PAM. Last, Cpf1 may be easier to deliver to cells, as it is smaller and does not require a tracrRNA.