GUMS (Grid User Management System) is a Grid Identity Mapping Service. Identity mapping is necessary when a site's resources do not use GRID credentials natively, but instead use a different mechanism to identify users, such as UNIX accounts or Kerberos principals. In these cases, the GRID credential for each incoming job must be associated with an appropriate site credential. The GUMS server performs this mapping upon request and returns the mapping to the gatekeeper. The gatekeepers are charged with enforcing the site mapping established by GUMS. GUMS is comprised of web services, web pages for GUMS administration, and command-line tools which interact with the web services. Typically, the term "GUMS" refers to the server portion.

GUMS is particularly well suited to a heterogeneous environment with multiple gatekeepers; it allows the implemenation of a single site-wide usage policy, thereby providing better control and security for access to the site's grid resources. Using GUMS, individual resource administrators are able to assign different mapping policies to different groups of users and define groups of hosts on which the mappings will be used. GUMS was designed to integrate with the site's local information services (such as HR databases or LDAP).

GUMS has been a production system at BNL since May 2004, managing gatekeepers for USATLAS, STAR and PHENIX. Current development, led by Jay Packard and John Hover, is centered on providing ease of use and completeness for both administrators and developers. Part of the development is dedicated to the VO Privilege Project, a collaboration between USATLAS and USCMS which is working to provide access to GUMS through the gatekeeper callout and role-based authentication through a VOMS extended proxy.