Referendums provide citizen control over policy outcomes under various institutional provisions. This paper offers a theoretical model covering four types of referendums, which differ with respect to their likelihood of occurring and their policy consequences. Implications derived from this model suggest that provisions that allow an opposition group to propose policies to be adopted by referendum should lead to more popular votes. Under these provisions policies adopted should also more closely reflect the policy preferences of the median voter. Support for these implications appears in data on American states and countries around the world.