Femtosecond transient absorption studies of [Os(bpy)(3)](2+) have been performed to gain new insights into the excited-state dynamics. Experiments were performed for a series of excitation wavelengths throughout both the singlet and triplet metal-to-ligand charge transfer (MLCT) bands. The dynamics are probed via the pi-pi* transition on the bpy(-) anion at 370 nm. Time scales for interligand electron transfer (ILET) and vibrational cooling are extracted from the amplitude and anisotropy of the excited state absorptions. The ILET rate has been measured as a function of temperature and, from these data, estimates for the electron transfer activation energy and ligand-ligand coupling are made. Our data also provide insight into the vibrational cooling dynamics within these large complexes, suggesting that vibrational cooling occurs only when exciting into the singlet MLCT state, after intersystem crossing. It appears that photoexcitation within the triplet MLCT absorption produces molecules that are vibrationally cold, even for excitation at the blue edge of the absorption band.