In 1987, Pasquier constructed the critical A-D-E lattice models whose partition functions are found to be identical to the modular invariant partition functions of unitary minimal models in conformal field theory. In this talk, I will introduce the A-D-E models and show how to construct new models from the existing ones by a process called fusion. The fusion procedure is used to construct integrable boundary conditions and to derive the functional equations which can be solved to give the spectra of the transfer matrices.