This is a description of the increasingly important technology of head-up displays. The book starts with the development of head-up displays, particularly specifications and standards, and operational problems associated with HUD use. HUD involvement in spatial disorientation and its use in recognizing and recovering from unusual attitudes is also discussed. The book summarizes the design criteria including hardware, software, interface and display criteria. It goes on to outline flight tasks to be used for evaluating HUDs and discusses the impact of HUDs on flight training. Recent work indicates that a HUD may allow a significant reduction in the time required to train a pilot on a particular craft, even considering non-HUD-related tasks. The author concludes with a review of unresolved HUD issues and recommendations for further research.