Post-functionalization of metal N-heterocyclic carbene complexes (metal NHCs) is described in this focused review. As metal NHCs are nowadays prominent in organometallic chemistry, functionalization methods for these scaffolds are of high importance for numerous applications of these organometallic compounds, ranging from catalysis to medicinal chemistry. Recently, post-functionalization – i.e. chemical modification of a preformed metal complex – has emerged as a set of divergent and modular methods for metal NHC modification. Examples chosen herein highlight that in a near future such methods may increase the number and diversity of biocompatible and bioconjugated metal–NHC complexes.