A high-level systematic computational Study is presented on all accurate Value for the adiabatic valence electron affinity of nitromethane, CH3NO2, to resolve literature disagreements ill theoretical and experimental reported Values. Density Functional methods with triple-zeta quality basis sets gave good fortuitous agreement to early experimental determinations, while single-reference wave function based methods employing Up to CCSD(T) gave poor or fortuitous agreement depending oil the experimental reference Value. DFT methods ill general cannot accurately describe electron attachment from the result Of unphysical self-interaction. It is found that multireference methods with aug-cc-pVTZ or similar basis sets are required to converge to fit experimental Value. Our highest level of theory 3S-MCQDPT2 and 7S-MCQDPT2 calculations with all aug-cc-pVTZ quality basis description yield values of 0.188 and 0.176 eV (0.170 eV with polynomial extrapolation), in excellent agreement with the most recent experimental Value of 0.172 +/- 0.006 eV. CCSD(T)//aug-cc-pVTZ provides a fortuitously reasonable description. The isolated dipole-bound anion binding energy is tentatively calculated to be 7-8 meV.