Orbitals rigorously defined on molecular fragments, like the extremely localized molecular orbitals, represent a possible way to build up the electronic structure of large molecules, using molecular fragments assembled on small molecules. Of course a rigorous localization is strictly connected to a reduction in the number of variational parameters, which reflects in an increasing value of the associated energy. In order to get both an extremely localized description of the molecule and an increase of the energetic accuracy, we have developed a method which allows a relaxation of the electronic structure based on localized orbitals. The relaxation is realized by means of a Valence Bond technique, which in turn uses the localized nature of the orbitals to reduce the number of excitations. Applications to the transferability of extremely localized molecular orbitals are presented.