Design engineers share archaeologists' interest in material culture, but unlike archaeologists, engineers have developed concepts for determining the suitability of technical systems to perform specific tasks. Given the difficulty archaeologists face in developing theories of material culture, the author suggests that guiding principles of engineering design offer potentially useful insights. In this article he discusses two design alternatives for optimizing the availability of any technical systemmreliability and maintainability. Reliable systems are made so that they can be counted on to work when needed. Maintainable ones can easily be made to function if they are broken or not appropriate to the task at hand. Because these design alternatives have markedly different optimal applications and observably different physical characteristics, archaeologists can link the design of prehistoric weapons to environmental constraints and to specific hunting strategies. Ethnographic examples indicate that primitive hunters do use both reliable and maintainable systems in optimal situations.