Modern head-up display (HUD) systems display flight information and guidance commands, in the form of electronic symbology and/or sensor imagery, so that they are visually coincident with the real world as seen from the cockpit. The basic virtue of head-up displays is that the pilot's visual and mental attention remains outside the cockpit in order to monitor available visual cues while viewing all critical instrument data. The HUD symbology is conformal with the real world and focused at infinity so that ocular transition between such data and the real world is eliminated. Such a system, when properly designed and employed, contributes greatly to safety, pilot confidence, reduced pilot workload, and more precise, accurate flying.This paper describes such a HUD guidance system and various approaches to the design of a pilot-in-the-active-control-loop head-up display system, HUD system architecture and aircraft sensor requirements. Additionally, general aviation applications, including possible symbology, will be addressed.