Since their discovery in 1968 by Öfele and Wanzlick, and their first isolation in the free state by Arduengo in the early 1990s, N-heterocyclic carbene (NHC) ligands have received a growing attention from the scientific community, notably in organometallic chemistry. These ligands are likely to surpass in popularity well-known phosphorus-based ligands because of their remarkable ability to establish strong bonds with the metal center and their capacity to permit significant doping of catalyst activity in a wide range of chemical transformations such as olefin metathesis, carbon-carbon and carbon-nitrogen cross-coupling reactions, hydrogenation, and hydrosilylation.