Three newly established public agencies built regional rail projects in Los Angeles County from 1978 to 2002. The Los Angeles County Transportation Commission, the Los Angeles Metropolitan Transportation Authority, and the Alameda Corridor Transportation Authority were experiments in regional governance. Conventional understanding of these agencies only partially explains their successes and failures. One path to improved understanding is to combine research on the politics of designing new public agencies with research on cooperation in collective action problems. What emerges is an untold story of American politics: the evolution of mechanisms that promote cooperation. Four findings emerge: (1) conflict is inevitable; (2) public agencies can succeed despite the problems of politics; (3) successful regional solutions are intensely local; and (4) cooperation emerges from supply-side mechanisms that create new resources rather than reallocate existing resources. The limits of politics are neither random nor predestined—neither is the governance solution.