The cyanate ion is an anion with the chemical formula . It is a resonance of three forms:  (61%) ↔  (30%) ↔  (4%).
Cyanate is the derived anion of isocyanic acid, H−N=C=O, and its lesser tautomer cyanic acid (a.k.a. cyanol), H−O−C≡N.
Any salt containing the ion, such as ammonium cyanate, is called a cyanate.
The cyanate ion is an isomer of the much-less-stable fulminate anion,  or .
The cyanate ion is an ambidentate ligand, forming complexes with a metal ion in which either the nitrogen or oxygen atom may be the electron-pair donor. It can also act as a bridging ligand.
Compounds that contain the cyanate functional group, −O−C≡N, are known as cyanates or cyanate esters. The cyanate functional group is distinct from the isocyanate functional group, −N=C=O; the fulminate functional group, ; and the nitrile oxide functional group,  or .