TWINS (Two-wide Angle Imaging Neutral-atom Spectrometer) is a mission consisting of two identical, widely-separated satellites, TWINS-A and TWINS-B, in high-altitude, high-inclination orbits which will enable the three-dimensional visualization and resolution of large-scale structures and dynamics within the Earth's magnetosphere. A MIDEX (Medium-class Explorer), TWINS will extend the detailed study of energetic neutral atoms in the magnetosphere which began with the IMAGE mission in 2000. TWINS instrumentation is essentially the same as the MENA (Medium-Energy Neutral Atom imager) instrument on IMAGE. However, the capability of TWINS to carry out stereo imaging will greatly extend understanding of magnetospheric structure and processes. The TWINS satellites are scheduled for launch in March 2005 (A) and March 2006 (B) into orbits with apogees of 7.2 Earth-radii and inclinations of 63.4°.