Bileptons - Status and Prospects

Theoretical backgound for bileptonic gauge bosons is reviewed, both the SU(15) GUT model and the 3-3-1 model. Then the mass limits for bileptons are discussed coming from $e^{+}{e}^{-}$ scattering, polarized muon decay and muonium-antimuonium conversion. A consequence of precision electroweak data on the masses is mentioned. Discovery in $e^{-}{e}^{-}$ at a linear collider is emphasised.