The invention relates to a disc tumbler cylinder lock and a key for it. The key according to the invention comprises a groove that is transverse to the key shank. The groove comprises a bottom section and side sections that are transverse to the bottom section between the bottom section and the outer surface of the key shank. The bottom section of the groove is the key's main driving surface used to transfer turning force to the disc tumbler cylinder lock. This reduces wear on the O-surfaces of the key because the O-surfaces do not transfer the majority or any of the key turning force to the disc tumbler cylinder lock.