In this talk I will present the Hamiltonian Truncation method, one of the simplest realizations of the ''exact diagonalization'' techniques used to solve strongly-coupled QFTs numerically, as opposed to standard lattice Monte Carlo methods. I will prove the feasibility of the method by applying it to a simple non-integrable model in two dimensions, and compare the obtained results with the literature. I will also comment on similar truncation methods and on future developments aimed at making this type of techniques a useful alternative to the lattice.