Chemistry freshmen learn to distinguish between nitrate NO3− and nitrite NO2− or sulfate SO42− and sulfite SO32−, but how many would know about carbonite CO22− in contrast to carbonate CO32−? This is not surprising for an anion that has never been observed in solution. However, it might be a crucial intermediate in the reductive activation of CO2. This review will track back carbonite and reflect on its relevance to carbon dioxide binding in metal complexes. Display omitted •This review describes carbonite, which is the dianion of carbon dioxide as well as the conjugated base of dihydroxycarbene.•Carbonite is considered an important intermediate in the reductive activation of CO2.•We discuss electronic und structural features of CO22− and its metal derivatives.