Laboratory and radiographic tests are often ordered unnecessarily. This excess testing has financial costs and is a burden on patients. We performed a systematic review to determine the effectiveness interventions to reduce test utilization by physicians. The MEDLINE and EMBASE databases were searched for the years 1946 through to September 2013 for English articles that had themes of test utilization and cost containment or optimization. Bibliographies of included papers were scanned to identify other potentially relevant studies. Our search resulted in 3236 articles of which 109 met the inclusion criteria of having an intervention aimed at reducing test utilization with results that could be expressed as a percent reduction in test use relative to the comparator. Each intervention was categorized into one or more non-exclusive category of education, audit and feedback, system based, or incentive or penalty. A rating of study quality was also performed. The percent reductions in test use ranged from a 99.7% reduction to a 27.7% increase in test use. Each category of intervention was effective in reducing test utilization. Heterogeneity between interventions, poor study quality, and limited time horizons makes generalizations difficult and calls into question the validity of results. Very few studies measure any patient safety or quality of care outcomes affected by reduced test use. There are numerous studies that use low investment strategies to reduce test utilization with one time changes in the ordering system. These low investment strategies are the most promising for achievable and durable reductions in inappropriate test use.