The author describes in this paper the creation and operation of the Open Science Grid (OSG ), a distributed shared cyberinfrastructure driven by the milestones of a diverse group of research communities. The effort is fundamentally collaborative, with domain scientists, computer scientists and technology specialists and providers from more than 70 U.S. universities, national laboratories and organizations providing resources, tools and expertise. The evolving OSG facility provides computing and storage resources for particle and nuclear physics, gravitational wave experiments, digital astronomy, molecular genomics, nanoscience and applied mathematics. The OSG consortium also partners with campus and regional grids, large projects such as TeraGrid , Earth System Grid , Enabling Grids for E–sciencE (EGEE ) in Europe and related efforts in South America and Asia to facilitate interoperability across national and international boundaries.
OSG’s experience broadly illustrates the breadth and scale of effort that a diverse, evolving collaboration must undertake in building and sustaining large–scale cyberinfrastructure serving multiple communities. Scalability — in resource size, number of member organizations and application diversity — remains a central concern. As a result, many interesting  challenges continue to emerge and their resolution requires engaged partners and creative adjustments.