In this thesis, the nature of the magnesium non-covalent interactions is investigated. Topological analysis of electron density indicates that magnesium bonds are closed-shell in nature. Also, the topology of the Laplacian of electron density shows that these bonds can be categorized as lump-hole interactions. In this point of view, these interactions are similar to halogen bonds, pnicogen bonds, beryllium bonds, and tetrel bonds. Indeed, there is a region of charge depletion around the Mg atom, which can interact with a region of charge concentration of an atom in the base and form a magnesium bond. A Comparison of magnesium bonds with the hydrogen bond and beryllium bonds indicates that these interactions are different in several aspects. To shed more light on the nature of magnesium bonds, different energy decomposition methods, including NEDA, LMOEDA, IQA, and IQF, are used to partition their interaction energies into physically meaningful components. NEDA and LMOEDA approaches show that the polarization and electrostatic terms are mainly responsible for the formation of magnesium bonds. On the other hand, IQA and IQF calculations indicate that covalent contributions in the magnesium interactions are non-negligible. Finally, the interactions between H 2 , NH 3, and CO molecules and magnesium clusters and also magnesium oxide clusters are studies .