Recent approaches in which at least two metal or main-group centres are involved in the homologation of CO are reviewed. We have characterised the strategies into three broad areas: (i) the reductive homologation of atmospheric CO at a metal or main group centre (ii) the reductive homologation of metal–carbonyl CO units and (iii) reductive homologation of CO with M–M, B–Li, SiSi, and BB bonds.