AbstractThe electrostatic potential V(r) that is created by a system of nuclei and electrons is formulated directly from Coulomb's law and is a physical observable, which can be determined both experimentally and computationally. When V(r) is evaluated in the outer regions of a molecule, it shows how the latter is ‘seen’ by an approaching reactant, and thus is a useful guide to the molecule's reactive behavior, especially in noncovalent interactions. However, V(r) is a fundamental property of a system, the significance of which goes beyond its role in reactivity. For example, the energy of an atom or molecule can be expressed rigorously in terms of the electrostatic potentials at its nuclei. These and other features of V(r) are discussed in this overview. © 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 153‐163 DOI: 10.1002/wcms.19This article is categorized under: Structure and Mechanism > Molecular Structures