The electronic structure of the X (2)Σ(+), A (2)Π, and B (2)Σ(+) states of aluminum monoxide (AlO) are studied via ab initio multi-reference configuration interaction calculations. Core correlation corrections, several basis sets, and active space choices are considered. Angular momentum and spin-orbit coupling terms are obtained at different levels of theory. The resulting ab initio curves are used to solve the associated rovibronic problem for the total angular momentum J up to 112.5 and then also refined by fitting to the experimental wavenumbers available in the literature, reproducing them with the root-mean-square error of 0.07 cm(-1). Theoretical rovibronic energy levels of AlO in its X (2)Σ(+), A (2)Π, and B (2)Σ(+) electronic states are presented including those from the X - B blue-green system.