Perturbation Theory (SAPT) has proven extremely successful for the study of weakly interacting dimers. Extending this approach beyond dimers to study systems with many interacting fragments is a focus of intense research efforts. Orbital-space-based Energy Decomposition Analysis (EDA) schemes, which are mostly based on the pioneering work of Morokuma, are also useful tools for the study of chemical interactions. However, their application is also limited to isolated fragment pairs. Real space quantification methods, typically based on the Quantum Theory of Atoms in Molecule (QTAIM), offer a promising avenue for unraveling the contribution from individual molecular interactions in complex systems, allowing for arbitrary fragment definitions.