  The discovery that a spin polarized current can exert a large torque on a
ferromagnet through a transfusion of spin angular momentum, offers a new way to
control a magnetization by simple current injection, without the help of an
applied external field. Spin transfer can be used to induce magnetization
reversals and oscillations, or to control the position of a magnetic domain
wall. In this review, we focus on this last mechanism, which is today the
subject of an extensive research, both because the microscopic details for its
origin are still debated, but also because promising applications are at stake
for non-volatile magnetic memories.
