The excited states of the gold dimer have been investigated using modern theoretical tools including the multiconfigurational exact molecular mean-field intermediate Hamiltonian Fock-space Coupled Cluster, X2Cmmf-IHFSCC, and the complete active space self-consistent field followed by second order perturbation theory, CASSCF/CASPT2. The computed optically active transitions have been benchmarked against the available experimental data and compared with time-dependent density functional theory, TDDFT, results, both in the two- and four-component schemes. We explored in great detail several spectroscopic properties such as bond lengths, potential energy surfaces (PES), vibrational frequencies and vibrational progressions of the ground and low-lying excited states. Our data show excellent agreement with the experimental measurements and present a significant improvement compared to previous ab initio calculations. They also permit a detailed investigation of the intriguing a ← X and A' ← X experimental bands that, according to our calculations, show an avoided energy level crossing. The location of this crossing is critical for a correct estimation of the vibrational progression and oscillator strengths of these two states. Moreover, among the exchange-correlation (xc) potentials, the SAOP gives the best excitation energies, followed by the hybrid B3LYP functional. Pure functionals like BLYP give by far the worst results.