Linkage isomerism is the existence of coordination compounds that have the same composition differing with the connectivity of the metal to a ligand.

Typical ligands that give rise to linkage isomers are:

Examples of linkage isomers are violet-colored [(NH₃)₅Co-SCN] and orange-colored [(NH₃)₅Co-NCS]. The isomerization of the S-bonded isomer to the N-bonded isomer occurs intramolecularly. In the complex, dichlorotetrakis(dimethyl sulfoxide)ruthenium(II), linkage isomerism of dimethyl sulfoxide ligands can be observed in the NMR spectrum due to the effect of S vs. O bonding on the methyl groups of DMSO. The proper notation for linkage isomerism is the kappa notation where the atom directly bonding to the metal is proceeded by the lowercase Greek letter kappa; κ. For example, NO₂ is represented as nitrito-κ-N and nitrito-κ-O, replacing the old system of trivial names such as nitro and nitroso.