In this paper, I present a newly developed model of the magnetic effects of field-aligned currents. The magnetic field of a large-scale field-aligned current system is obtained by summing the magnetic fields of a large number of finite length cylindrical current elements. The resulting magnetic field is valid inside of, near and far away from the model field-aligned currents, both near the ionosphere and in the magnetosphere. The modeling technique allows for the closure of the field-aligned currents along any specified path. In order to investigate the effects of field-aligned currents on the nightside magnetospheric magnetic field and on mapping between the night-side magnetosphere and ionosphere, I add the effects of region I and II field-aligned currents to an empirical magnetic field model. Using this model, I demonstrate the following three things: (1) reasonable amounts of field-aligned current can cause the ionospheric footprint of a point at geosynchronous orbit to shift in local time by one hour or more; (2) depending on how they are closed, field-aligned currents can cause Bz in the equatorial plane, near midnight, either to increase or to decrease; (3) CPS field lines can cross the equatorial plane 10 RE or more further from the noon-midnight meridian than they would if field-aligned current effects were not included, a result that also depends on how the currents are closed. ¿ American Geophysical Union 1993