The COP9 signalosome (CSN) is a platform for protein communication in eukaryotic cells. It has an intrinsic metalloprotease that removes the ubiquitin (Ub)‐like protein Nedd8 from cullins. CSN‐mediated deneddylation regulates culling‐RING Ub ligases (CRLs) and controls ubiquitination of proteins involved in DNA damage response (DDR). CSN forms complexes with CRLs containing cullin 4 (CRL4s) which act on chromatin playing crucial roles in DNA repair, checkpoint control and chromatin remodeling. Furthermore, via associated kinases the CSN controls the stability of DDR effectors such as p53 and p27 and thereby the DDR outcome. DDR is a protection against cancer and deregulation of CSN function causes cancer making it an attractive pharmacological target. Here we review current knowledge on CSN function in DDR.