Metropolitan planning organizations (MPOs) are often the conduit through which billions of federal and state transportation dollars flow for regional transportation investments. Decisions by MPOs have important ramifications for metropolitan growth patterns and, by implication, social and economic opportunity. Yet, the decisions are made by boards whose members are generally not elected to serve on the MPO. Further, MPOs are not required by law to have representational voting. The potential exists, therefore, for MPO decisions to be biased toward certain constituencies or locales at the expense of others. This policy brief reviews MPOs generally and discusses the variation in MPO voting structures—with implications for potential bias—in 50 large metropolitan areas.