Fault-injection involves the deliberate insertion of faults or errors into a computer system in order to determine its response. It has proven to be an effective method for measuring the parameters of analytical dependability models, validating existing fault-tolerant systems, synthesizing new fault-tolerant designs, and observing how systems behave in the presence of faults. Growing dependence on computers in life- and cost-critical applications makes it increasingly important to understand and utilize this technique. This paper motivates the use of fault- injection and develops a taxonomy for interpreting fault-injection experiments. Background on how faults affect computer systems is provided. Results from several recent fault-injection studies are reviewed. Tools that facilitate the use of fault-injection are examined, and areas for future research are discussed.