Current-driven domain-wall motion and related phenomena are reviewed from a theoretical point of view. In the first part, the dynamics of a rigid domain wall is described based on the collective-coordinate method. After an elementary introduction, the equations of motion are derived for a wall under current, whose effects enter as a spin-transfer effect and a momentum-transfer effect (force). The wall motion is studied in detail, and several depinning mechanisms are found. In the second part, a microscopic derivation of spin torques is described for slowly varying magnetic texture. In addition to the well-established spin-transfer torque, two new torques are shown to arise from the spin-relaxation process and the nonadiabatic process (reflection) of conduction electrons. These new torques act as forces on a rigid wall. Some related topics are described in the third part, which includes current-driven dynamics of magnetic vortices and the current-induced spin-wave instability and domain-wall nucleation.