  We introduce a novel method for the renormalization of the Hamiltonian
operator in Quantum Field Theory in the spirit of the Wilson renormalization
group. By a series of unitary transformations that successively decouples the
high-frequency degrees of freedom and partially diagonalizes the high-energy
part, we obtain the effective Hamiltonian for the low energy degrees of
freedom. We successfully apply this technique to compute the 2-loop
renormalized Hamiltonian in scalar $\lambda \phi^4$ theory.
