Manganese–hydroxo species have been implicated in C–H bond activation performed by metalloenzymes, but the electronic properties of many of these intermediates are not well characterized. The present work presents a detailed characterization of three Mnn–OH complexes (where n = II, III, and IV) of the tris[(N′-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3–) ligand using X- and Q-band dual mode electron paramagnetic resonance (EPR). Quantitative simulations for the [MnIIH3buea(OH)]2– complex demonstrated the ability to characterize similar MnII species commonly present in the resting states of manganese-containing enzymes. The spin states of the MnIII and MnIV complexes determined from EPR spectroscopy are S = 2 and 3/2, respectively, as expected for the C3 symmetry imposed by the [H3buea]3– ligand. Simulations of the spectra indicated the constant presence of two MnIV species in solutions of [MnIVH3buea(OH)] complex. The simulations of perpendicular- and parallel-mode EPR spectra allow determination of zero-field splitting and hyperfine parameters for all complexes. For the MnIII and MnIV complexes, density functional theory calculations are used to determine the isotropic Mn hyperfine values, to compare the excited electronic state energies, and to give theoretical estimates of the zero-field energy.