This paper describes the broad goals and the current status of the Space Interferometry Mission (SIM). SIM was endorsed in the 1990 decadal report of the Astronomy and Astrophysics survey committee of the National Research Council. The SIM mission would be the first long baseline interferometer in space. The goals of SIM represent not factors of two or three improvement in astronometric accuracy, but two to three orders of magnitude improvement. The current most accurate astrometric measurements are from the Hipparcos satellite launched by ESA in 1990. Hipparchos achieved slightly better than 1 milliarcsec global astrometric accuracy. SIM's goal is 4 microarcsec accuracy for global astrometry (for a nominal 5 yr mission) and 1 microarcsec for single measurement narrow angle accuracy. The narrow angle precision translates to the ability to measure the "wobble" of stars with an error of 0.14 uas, if the target is observed 50 times during the 5 year mission. The paper gives an overview of the type of scientific questions SIM will address, concentrating on the planet detection aspects of SIM.