Since the detection of O+ ions by satellites in the 1970s it has been known that the ionosphere is an important source of plasma in the Earth’s magnetotail. More recent observations from have shown that these ions can become a dominant component of the plasma in the plasmasheet. Early work in substorm research considered a role for O+ in the onset of plasma instabilities and their relationship to substorm onset. Theoretical analysis of reconnection in multi-fluid plasmas has shown that the presence of a heavy ion slows the reconnection rate raising interesting implications for occurrence rate of substorms. Global scale simulations have been used effectively to model the interaction of the solar wind with the tightly coupled magnetosphere-ionosphere-thermosphere system. These models are now beginning to utilize multi-fluid techniques to include mass outflows from the ionosphere. Techniques for including these outflows include both empirical and first principle models. In the empirical techniques the relationship between observed parameters such as Poynting flux and outflow are used to specify both the location and intensity of the outflow seen in the cusp and auroral regions. First principle models of the polar wind typical use a large set of single flux tubes simulations describe the out flowing plasma. In both approaches significant impacts on the state of the magnetosphere is seen when the ionospheric plasma is included. These affects include improved agreement with Dst observations, changes in polar cap potential, and alteration of the length of the magnetotail. Furthermore, some simulation results have demonstrated a role for O+ in the transition from steady magnetospheric convection into the sawtooth intervals containing multiple storage and release segments.