This paper examines the competitive effects of charter schools on the efficiency of traditional public schools. The analysis utilizes a statewide school-level longitudinal dataset of Michigan schools from 1994 to 2004. Fixed effect and two alternative estimation methods are employed. Overall, the results suggest that charter competition had a negative impact on student achievement and school efficiency in Michigan's traditional public schools. The effect is small or negligible in the short run, but becomes more substantial in the long run. (Contains 9 tables.)