  Non-perturbative renormalization of lattice composite operators plays a
crucial role in many applications of lattice field theory. We sketch the
general problems involved in this task and the methods which are currently used
to cope with them. We present a detailed investigation of a new approach based
on the operator product expansion. We test the new method on the
two-dimensional O(3) sigma-model and discuss its advantages and limitations.
Ph.D. thesis at Scuola Normale Superiore, Pisa, Italy.
