Even the most sophisticated missile defense interceptors cannot complete their mission effectively without the ability to see their target. While sensors and command and control often get short shrift in discussions of missile defense in favor of interceptor improvements, upgrading the sensor architecture offers another effective means to improve the overall function of the BMDS. Particular attention to the issue of midcourse discrimination will be essential to enhance the capabilities of currently fielded GMD interceptors, whether those sensors are deployed in space, in the air, on the ground, or at sea.