Advanced theoretical methodologies and photoelectron photoion coincidence spectroscopy were used to investigate the photoionization of ethanolamine in the 8-18 eV energy range. We identified the low-lying cation conformers and the excited cation electronic states after vertical excitation from the most stable neutral conformer computationally. The TPES is composed of broad, structureless bands because of unfavorable Franck-Condon factors for origin transitions upon ionization, populating the D₀-D₇ cationic states from the most stable neutral conformer, g′Gg′. The adiabatic ionization energy of ethanolamine is calculated at 8.940 ± 0.010 eV, and the 0 K appearance energies of aminomethylium, NH₂CH₂⁺ (+CH₂OH), and methyleneammonium, NH₃CH₂⁺ (+H₂CO), are determined experimentally to be 9.708 ± 0.010 eV and 9.73 ± 0.03 eV, respectively. The former is used to re-evaluate the ethanolamine enthalpy of formation in the gas and liquid phases as Δ_fH^⊖_298K[NH₂(CH₂)₂OH, g] = −208.2 ± 1.2 kJ mol⁻¹ and Δ_fH^⊖_298K[NH₂(CH₂)₂OH, l] = −267.8 ± 1.2 kJ mol⁻¹. This represents a substantial correction of the previous experimental determination and is supported by ab initio calculations.