Raman spectroscopy has been used to elucidate the structure of molten iron(III) chloride and its binary mixtures with caesium chloride. In order to overcome difficulties arising from the dark coloration of these melts and to ensure the spectral features, both conventional resonance Raman and micro-Raman spectra have been obtained. The spectral changes upon melting the solids Cs₂NaFeCl₆, CsFeCl₄ and FeCl₃ have also been measured. The FeCl₄^- tetrahedra were found to be present in both the solid and molten CsFeCl₄, while a change of coordination from six-fold (FeCl₆^3-) to four-fold (FeCl₄^-) occurs upon melting Cs₂NaFeCl₆. The FeCl₄^- tetrahedra are the predominant species in CsCl–FeCl₃ mixtures containing up to 50 mol% FeCl₃. The systematics and the temperature dependence of the spectra of the molten mixtures with mole fractions from 50 to 100 mol% FeCl₃ indicate the presence of Fe₂Cl₇^-, FeCl₂⁺ and Fe₂Cl₅⁺ ionic species. Resonance Raman spectra of molten FeCl₃ were measured and compared with the spectra of the corresponding solid and vapor. The data are interpreted to indicate a self-ionization of the molecular Fe₂Cl₆ melt: 2Fe₂Cl₆Fe₂Cl₅⁺ +Fe₂Cl₇^-. The proposed model accounts for both the near-ionic conductivity of the melt and the structural data obtained by neutron diffraction.