Determining who is a member of your virtual organization (VO) and who can access and use its resources is a critical area known as identity management. As Mine Altunay wrote in August, OSG is evolving its identity management strategy, adapting to a number of technological changes and increased understanding of the requirements. The eXtreme Scale Identity Management (XSIM) project at Indiana University, funded by the Department of Energy’s Next Generation Networks for Science program, and an OSG satellite project, is studying how VOs and resource providers work together to do identity management and is now providing guidance based on the results of that research. To support the OSG efforts, XSIM developed a guidance document for OSG VOs and resource providers to provide guidance on different options for implementing trust between a VO and resource provider. XSIM is happy to consult with VOs and resource providers on this topic and welcomes feedback on the document.