N-heterocyclic carbenes (NHCs) have become powerful organic catalysts for polymer synthesis.1 This relates to the possibility for finely tuning their steric and/or electronic properties.Yet,their rather high reactivity makes NHCs difficult to handle.We have shown that both molecular and polymeric versions of imidazol(in)ium hydrogen carbonates (see Figure) behave as air-stable NHC precursors,enabling facile organocatalyzed molecular reactions and metal-free polymer synthesis as well,e.g.for group transfer polymerization (GTP) of methyl methacrylate (MMA) or ring-opening polymerization (ROP) of D,L lactide.