This chapter discusses the interaction between currents and magnetization, which can cause undesirable effects such as enhanced magnetic noise in read heads made from magnetic multilayers. While most research has been carried out on metallic structures, current-induced magnetization dynamics in semiconductors or even insulators has been pursued as well. These issues have attracted many physicists because, on top of the practical aspects, the underlying phenomena are fascinating. Berger and Slonczewski are acknowledged to have started the field in general through their introduction of the concept of current-induced magnetization dynamics by the transfer of spin. The reciprocal effect, i.e., spin pumping, was expected long ago, but it took some time before Tserkovnyak et al. developed a rigorous theory of spin pumping for magnetic multilayers, including the associated increased magnetization damping.