To address these challenges, various methodologies have been developed. Multicomponent methods stand out, o↵ering a way to handle nuclei and electrons quantum mechanically on the same level, thus inherently including anharmonic e↵ects, nuclear delocalization, zeropoint vibrational energies (ZPVE), and quantum tunneling. Historical contributions from Thomas and pioneering works by Parr and Gross have led to the development of several branches and implementations of this multicomponent treatment, such as the dynamical extended molecular orbital (DEMO), nuclear orbital molecular orbital (NOMO), mul-ticomponent molecular orbital (MCMO), electronic and nuclear molecular orbitals (ENMO) approaches as well as the most commonly discussed framework today, the nuclear electronic orbital (NEO) approach. We recognise that the similarities between the di↵erent implementations are greater in number than the di↵erences, but in lack of a consensual nomenclature we opt for the use of the NEO acronym in the following text.