Galactic Structure with SIM Carl Grillmair Spitzer Science Center Caltech Initially conceived as a technology demonstrator for the Terrestrial Planet Finder, the Space Interferometry Mission will be launched in 2010 on a 5 year mission to obtain pointed microarcsecond astrometry of stars and other targets to V>20. I will discuss the current status of SIM, along with the goals and preparatory work being carried out in support of the Galactic Structure Key Project.