One of the prototype compounds for metal-metal multiple bonding, the Re2Cl82- ion, has been studied theoretically using multiconfigurational quantum chemical methods. The molecular structure of the ground state has been determined. It is shown that the effective bond order of the Re-Re bond is close to three, due to the weakness of, in particular, the delta bond. The electronic spectrum has been calculated with the inclusion of spin-orbit coupling. Observed spectral features have been reproduced with good accuracy, and a number of new assignments are suggested.