Abstract: A method whereby application and network services (such as access control and electronic mailing list servers) can use a directory service to define groups of directory members using a directory search specification evaluated at service delivery time (dynamic group membership.) Traditionally, network services have been delivered to groups of users defined in relatively narrow manners: either by keeping a list of all users who are members of the group, or by attaching specific group membership attribute information to the information maintained about each specific user. Dynamic group membership allows these services to be delivered to groups of users who can be defined by a completely arbitrary specification of user attribute information. For example, electronic mail can be sent to a group of users whose office was located in a certain building (specifically, whose office location attribute matched a specific value.