  The COntractor REnormalization group (CORE) method, a new approach to solving
Hamiltonian lattice systems, is introduced. The method combines contraction and
variational techniques with the real-space renormalization group approach. It
applies to lattice systems of infinite extent and is ideal for studying phase
structure and critical phenomena. The CORE approximation is systematically
improvable and can treat systems with dynamical fermions. The method is tested
using the 1+1-dimensional Ising model.
