We generalise the notion of coherent states to arbitrary Lie algebras by
making an analogy with the GNS construction in $C^*$-algebras. The method is
illustrated with examples of semisimple and non-semisimple finite dimensional
Lie algebras as well as loop and Kac-Moody algebras.
A deformed addition on the parameter space is also introduced simplifying
some expressions and some applications to conformal field theory is pointed
out, e.g. are differential operator and free field realisations found.
PACS: 02.20.S, 03.65.F, 11.25.H
Keywords: coherent states, Lie and Kac-Moody algebras, realisations.