The auroral ionosphere is a region of intense energy precipitation. Its most noteworthy effects are the intense luminous emissions observed in the auroral oval. Less visible but of primary importance for magnetospheric dynamics, this energy precipitation results in an intense outflow of ionospheric ions. In this chapter, we provide an overview of the whole chain of processes associated with auroral ion outflow. We discuss the processes that energize ionospheric ions, from the topside ionosphere to the more distant magnetospheric regions, and the effect of auroral ionospheric outflow on the magnetospheric dynamics. We will also present recent observations of auroral ion outflow. They provide a detailed picture of its large-scale spatial distribution, its dependence on solar and geomagnetic activity, its temporal dynamics, and its connection with auroral emissions. © 2016 by the American Geophysical Union. All rights reserved.