The thermopower, the so-called Seebeck effect, is the conversion of heat to electricity and is due to the entropy carried by conduction electrons. In strongly-correlated electron systems and Kondo materials, spin fluctuation is shown to bring about an entropy in conduction electrons and to result in a giant thermopower. Recently, the spin Seebeck effect, which reflects the conversion via the spin current in magnetic materials, was discovered. The mechanism is examined and a variety of experiments are explained. © 2013 The Korean Physical Society.