A review has been given from a theorist point of view on the study of double oxide surfaces. Among wide classes of the related materials, focusing was made on the transition-metal oxides (TMO) particularly with the perovskite structure. The materials covered in this review are BaTiO₃ (ferroelectric), SrTiO₃ (quantum paraelectric), Sr₂RuO₄ (p-wave superconductor), La_1-xSr_xMnO₃ (colossal magnetoresistance) and TiO₂ (photocatalyst). The last one, which is neither double oxides nor perovskite, was included because it is the system that has been most intensively studied among TMO. It is pointed out that TMO is generally regarded as a strongly correlated system and that the symmetry lowering and dimension lowering by creating the surface can cause dramatic changes in the electronic and magnetic properties near the surfaces.