The potential energy functions of the aluminum dimer, Al2, in its lowest‐energy electronic states, X and A have been determined from ab initio calculations using the multi‐reference averaged coupled‐pair functional method in conjunction with the correlation‐consistent basis sets up to septuple‐zeta quality. The core‐electron correlation, scalar relativistic, and spin‐orbit effects were taken into account. The vibration‐rotation energy levels for both the states of Al2 were calculated to near the “spectroscopic” accuracy. The state was unequivocally confirmed to be the electronic ground state of Al2, and the electronic term value of the state was predicted to be 247 cm−1. The energies and intensities of direct electronic‐vibration transitions X ↔ A were predicted.