Spin conversion is a generic term for all the conversion phenomena based on the principle of angular momentum conservation, including recently discovered phenomena, i.e. the spin Hall effect, the inverse spin Hall effect, the spin Seebeck effect, the spin Peltier effect, the pure spin current induced magnetic switching, the spin injection into insulators, the electric field controlled magnetic anisotropy in ultra-thin ferromagnetic films, and so on. Most of the above-mentioned spin conversion phenomena take place at simple nano-scale interfaces between two different materials of magnets, non-magnets, semiconductors, or insulators. So that spin conversion phenomena are versatile for designing device functionalities in spintronic applications. In this seminar, we will show some of our efforts to realize new spin conversion properties by exploiting the surface state of topological insulator, metal/oxide interfaces, and superconductors.