Consequently, this leads to the emergence of an electron-deficient or electrophilic region known as a σ-hole. Experimental evidence of this phenomenon was reported as early as 1819 by Pelletier and Caventou when they found attractive interactions between dihalogens and anions. However, it was theoretical studies conducted by Politzer and Murray in the 1990s which provided explicit insights into the origin and electronic properties of the σ-hole, ultimately describing the entity as the result of an anisotropic charge distribution on the surface of a covalently bound halogen atom. These theoretical findings sparked curiosity and laid a foundation for further research carried out in the early 2000s, confirming the findings of Politzer and Murray. The interest surrounding the σ-hole culminated in an initiative led by the International Union for Pure and Applied Chemistry (IUPAC) aimed at taking a comprehensive look at intermolecular interactions involving halogens as electrophilic species. The project concluded in 2013, ultimately defining a halogen-bond (XB) interaction as a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same molecular entity. While the σ-hole model has been widely employed to explain the strength of XB, recent studies reveal that other components, such as electrostatics, charge transfer (CT), polarisation, and dispersion, play crucial roles in providing a complete understanding of these interactions. In 2021, the existence of the σ-hole was experimentally demonstrated using Kelvin probe force microscopy, providing tangible evidence for a theory that has been postulated for more than a century. This cutting-edge technique allowed the direct imaging of the asymmetric electronic charge distribution and the shape of the σ-hole in a brominated molecule, marking a significant milestone in the field of σ-hole interactions.