Oxazoline is a five-membered heterocyclic chemical compound containing one atom each of oxygen and nitrogen. It was first characterised in 1889 and was named in-line with the Hantzsch–Widman nomenclature. It is part of a family of heterocyclic compounds, where it exists between oxazole and oxazolidine in terms of saturation. Oxazoline itself has no current applications however compounds containing the ring, which are referred to as oxazolines or oxazolyls, have a wide variety of uses; particularly as ligands in asymmetric catalysis, as protecting groups for carboxylic acids and, increasingly, as monomers for the production of polymers.