This paper presents a comprehensive impedance spectroscopy comparison of the AC properties of dense stoichiometric TiO₂ and conductive Ti_nO_{2n − 1} Magnéli phases over a broad temperature range (up to 1000 °C for TiO₂ and 375 °C for Ti_nO_{2n − 1}). The frequency dependent conductivity and permittivity of both materials is explained in terms of “universal” power law behaviour. A deviation from the law, with a giant relative permittivity which is largely independent of frequency from 0.1 Hz to 100–200 kHz is observed in the case of Ti_nO_{2n − 1,} due to the presence of residual TiO₂ generating an Internal Barrier Layer Capacitor (IBLC) effect. The real–imaginary impedance plots are interpreted using an RC model and allow separation of the contribution of the grain bulk and the grain boundaries to the total resistivity of the material. In the case of the Ti_nO_{2n − 1} based materials this confirms that the IBLC effect is generated by insulating grain boundaries. The conduction mechanism in both TiO₂ and Ti_nO_{2n − 1} appears to be dominated by electronic conductivities, activated mainly through shallow donor levels up to 200 °C and over the entire band gap, which is narrower for Ti_nO_{2n − 1,} above 200 °C. A deeper understanding of the AC properties of Magnéli phases of Ti at different temperatures aids in the optimisation of electrical properties for a variety of sensor and electrical applications.