The block-localized wavefunction (BLW) method combines the advantages of both molecular orbital (MO) and valence bond (VB) theories and can be regarded as the simplest ab initio VB method. It can derive the wavefunction for an electron-localized (diabatic) state and thus can critically evaluate the impacts of electron transfer on molecular geometry and energetic and spectral properties. The energy decomposition approach based on the BLW method, or BLW-ED, can decompose non-covalent interactions in terms of a series of physically meaningful energy components, including polarization and charge transfer energy terms. In this chapter, we showcase the applications of the BLW method and BLW-ED approach to a broad range of non-covalent interactions, notably including hydrogen and halogen bonding, in an attempt to provide a unified picture for the forces governing various non-covalent interactions.