Engineers and managers need information about reliability before making important product design and product release decisions. A reliability demonstration test shows-with a specified level of statistical confidence-the reliability meets a target value. It uses test results to determine a lower statistical confidence bound on reliability. If this bound equals or exceeds the target, demonstration is achieved. Demonstrating high reliability for a complicated system is difficult with tests of reasonable size and length. System reliability models are, therefore, used to assess reliability. The reliabilities of the system's life limiting components provide important inputs to such models. This article focuses on zero failure tests - that is, reliability demonstration is achieved only if no units fail.