Metropolitan public transportation systems vary in their performance and governance, and evidence suggests linkages between these. However, such linkages remain largely untested due to the complexity of governance and the absence of reliable and valid measures of it. We develop a conceptual framework for understanding metropolitan public transportation system governance using the familiar concepts of polycentricity and fragmentation. We introduce the novel concept of governance topology to parse the complexity of the many organizational arrangements and interorganizational relationships that comprise metropolitan governance. We then propose a method of measurement using a concentration index, and apply it to the Chicagoland region.