  We consider some unitary representations of infinite dimensional Lie algebras
motivated by string theory on AdS_3. These include examples of two kinds: the
A,D,E type affine Lie algebras and the N=4 superconformal algebra. The first
presents a new construction for free field representations of affine Lie
algebras. The second is of a particular physical interest because it provides
some hints that a hybrid of the NSR and GS formulations for string theory on
AdS_3 exists.
