Sixteen electronic states of Al2P2, three states of Al2P2+, and the ground state of Al2P2- are studied using the complete active-space MCSCF (CASSCF) followed by multireference singles + doubles configuration interaction (MRSDCI). The (1)A(g), B-2(1u), and B-2(1g) electronic states with rhombus equilibrium structures were found to be the ground states of Al2P2, Al2P2+, and Al2P2-, respectively. Alternative structures such as T-shaped, linear, and trapezoidal structures were considered, but the equilibrium geometry of the ground state was found to be the rhombus structure. Our computed results are compared with anion photoelectron spectroscopic studies of Neumark and co-workers. Comparison of electronic states of M2P2 (M = Al, Ga, and In) was made. It is shown that the electronic states of In2P2 exhibit anomalies due to relativistic effects.