Rapid progress in thermoelectric performance of oxide materials has been conducted virtually exclusively in Japan, resulting in more than ten times increase in the ZT values of oxides within the last two decades. This has caused a revolutionary change in the guiding principles of thermoelectric materials research, in which oxide materials had been disregarded as a potential candidate until early 1990s. Promising oxide thermoelectric materials having been discovered include CaMnO 3 -based perovskites, Al-doped ZnO, layered cobalt oxides represented by NaCo2O4 and Ca3Co4O9, and SrTiO 3 -related phases. This chapter reviews the current aspects of bulk oxide thermoelectric materials, and some strategies for selective reduction of the lattice thermal conductivity (selective phonon scattering) in bulk oxides are also discussed.