Multiconfiguration nonclassical-energy functional theory (MC-NEFT) 1,2,3 is a low-cost and high-accuracy electronic structure method to recover dynamic correlations in inherently multiconfigurational species. In MC-NEFT, one starts with a multiconfigurational wave function, usually a multiconfiguration self-consistent-field (MCSCF) wave function, such as a complete active space self-consistent field (CASSCF) wave function, 4 that recovers the static correlation and typically a small portion of the dynamic correlation. Then, a nonclassical energy functional is used to calculate the energy from some properties of the multiconfigurational wave function. The use of a nonclassical energy functional greatly reduces the computational cost compared to traditional post-CASSCF methods such as second-order complete active space perturbation theory (CASPT2), multireference Møller-Plesset perturbation theory, or multireference configuration interaction while having comparable or better accuracy in terms of bond dissociation energy, reaction barrier height, excitation energies, or other chemical properties. In recent years, we and coworkers have developed various versions of MC-NEFT, including multiconfiguration pair-density functional theory (MC-PDFT), multiconfiguration density-coherence functional theory (MC-DCFT), and multiconfiguration data-driven functional methods (MC-DDFMs), including hybrid versions of MC-PDFT and MC-DCFT. The ultimate goal of these theories is to achieve chemical accuracy at a cost that is affordable even for complex systems.