The mechanism of the dc electrical conduction and breakdown of perovskite-type titanates was investigated by impedance analysis. Based on an acceptor doped SrTiO3 model material, samples of different microstructures-ceramics, single crystals, and thin films-were employed. This approach allows us to distinguish conduction contributions of the bulk lattice, grain boundaries, and electrode interfaces. Based on defect chemistry studies, a predominant ionic contribution due to mobile oxygen vacancies and an additional p-type conduction were revealed for the bulk. At interfaces, space charge depletion layers of 100-500 nm width are formed in which the local conductivity is reduced by approx. four orders of magnitude compared to the bulk. Thin films show a similar depression of the conductivity. The combination of these facts may be indicative for considering thin films as distributed Schottky barriers. The field enhancement of the conductivity of thin films and of the interface depletion layers is compared and discussed.