The electronic structures of the cluster compound alpha-Nb3Cl8 and the intercalated phase beta’-NaNb3Cl8 have been studied by core level and valence band X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), diffuse reflectance spectroscopy, and charge-self-consistent molecular orbital (CSC-EH) and band structure (CSC-EH-TB) calculations. The crystal structures of the two compounds consist of layers of interconnected Nb3Cl13 units, XP and UP valence band spectra as well as the band structure calculations show well separated sets of Cl 3p levels at lower energy (higher binding energy) and Nb 4d levels at higher energy (lower binding energy), indicative of mainly ionic Nb-Cl bonding. The UP spectra of alpha-Nb3Cl8 reveal a triple-peak structure for the Nb 4d levels, corresponding to the 1a(1), 1e, and 2a(1) metal-metal bonding orbitals of a seven-electron Nb-3 cluster as suggested by theory. The valence band shapes are in good agreement with the theoretical density-of-states curve. The relative intensities in the XP valence band spectra of beta’-NaNb3Cl8 evidence an additional electron in the Nb 4d orbitals. The better resolved UP spectra, however, show a broad pattern for the Nb 4d levels which is neither expected from a single cluster model nor given by the theoretical density-of-states curve, Possible origins for this discrepancy between experiment and theory are discussed, Electrostatic interactions between Na+ and Cl- ions in beta’-NaNb3Cl8 lead to a narrowing of the Cl 3p core level and C1 3p valence band signals, the former being shifted to higher binding energy in comparison to alpha-Nb3Cl8. Two rather narrow absorptions in the optical spectra of alpha-Nb3Cl8 are assigned to the transitions from the 1a(1) and 1e levels into the singly occupied 2a(1) orbital. These absorptions are missing in the optical spectra of beta’-NaNb3Cl8, in agreement with the theoretical expectations for an eight electron Nb-3 cluster.