Interfaces (grain boundaries and surfaces) are studied in acceptor (Fe) doped SrTiO3 bicrystals, single crystals, and ceramics as a function of temperature (423 K less than or equal to T less than or equal to 1023 K), oxygen partial pressure (1 Pa less than or equal to p(O2) less than or equal to 10(5) Pa), and Fe doping content (1.9.10(18) cm(-3) less than or equal to c(Fe) less than or equal to 9.5.10(19) cm(-3)) using electrochemical methods. In particular, Impedance spectroscopy ve been applied. The electrochemical investigation of tilt and twist grain boundaries in bicrystals combined with structural and chemical grain boundary charactization by transmission electron microscopy, electron diffraction x-ray analysis, and electron energy loss spectroscopy allowed us to clarify grain boundary effects in SrTiO3. The use of reversible (nonblocking) YBa2Cu3O6+x electrodes proves to be a convenient technique to measure conductivities without electrode effects, since blocking effects at the sample surface were minimized. These results have been compared with those obtained for grain boundaries in polycrystalline samples as well as with the interfaces between metallic electrodes and SrTiO3 single crystals. Besides individual features, all findings at the investigated boundaries and interfaces could be consistently explained by the appearance of pronounced Schottky barriers which were composed of depletion layers of mobile majority charge carriers (h(.), V(o) double over dot).