In chemistry, linkage isomerism or ambidentate isomerism is a form of isomerism in which certain coordination compounds have the same composition but differ in their metal atom's connectivity to a ligand.

Typical ligands that give rise to linkage isomers are:

• thiocyanate, SCN⁻ – isothiocyanate, NCS⁻
• selenocyanate, SeCN⁻ – isoselenocyanate, NCSe⁻
• nitrite, NO−2
• sulfite, SO2−3

Examples of linkage isomers are violet-colored [(NH₃)₅Co-SCN]²⁺ and orange-colored [(NH₃)₅Co-NCS]²⁺. The isomerization of the S-bonded isomer to the N-bonded isomer occurs intramolecularly.

The complex cis-dichlorotetrakis(dimethylsulfoxide)ruthenium(II) (RuCl₂(dmso)₄) exhibits linkage isomerism of dimethyl sulfoxide ligands due to S- vs. O-bonding. Trans-dichlorotetrakis(dimethylsulfoxide)ruthenium(II) does not exhibit linkage isomers.