Quantum field theories on null surfaces

We study the behavior of quantum field theories defined on a surface S as i t tends to a null surface S-n. In the case of a real, free scalar field the ory the above limiting procedure reduces the system to one with a finite nu mber of degrees of freedom. This system is shown to admit a one parameter f amily of inequivalent quantizations. A duality symmetry present in the mode l can be used to remove the quantum ambiguity at the self-dual point. In th e case of the nonlinear sigma -model with the Wess-Zumino-Witten term a sim ilar limiting behavior is obtained. The quantization ambiguity in this case however cannot be removed by any means.