A computational study of the ground- and excited-state properties of the mixed-valence complex [(NH3)(5)(RuNCRuII)-N-III(CN)(5)](-) is presented. Employing DFT and TDDFT calculations for the complex in the gas phase and in aqueous solution, we investigate the vibrational and electronic structure of the complex in the electronic ground state as well as the character of the electronically excited states. The relevance of the various excited states for the intervalence metal-metal charge-transfer process in the complex is analyzed based on the change of charge density, spin density, and dipole moment upon photoexcitation as well as by a Mulliken-Hush analysis. Furthermore, those intramolecular modes, which are important for the charge-transfer process, are identified and characterized.