Group Member

A Group Member in Salesforce (GroupMember in the API) is a standard junction object that records a single membership relationship between a Group and either a User or another Group. Each Group Member record holds a GroupId (the parent Group — Public Group, Queue, Chatter Group, or any other system-managed group), a UserOrGroupId (the polymorphic member reference, pointing to either a User or another Group), and standard system fields. Groups in Salesforce are nestable — a Public Group can contain other Public Groups as members, and Group Member captures each level of that nesting one row at a time. Group Member is the underlying data structure behind nearly every group-based Salesforce feature: Public Group sharing rules iterate over Group Members to determine record visibility; Queue assignment routes records to Group Members; Chatter Group membership controls who can post and read; folder-access lists evaluate against Group Members. Every "who is in this Group?" question in Salesforce ultimately resolves to a Group Member SOQL query.

The UserOrGroupId field is polymorphic and accepts either a User Id or a Group Id. Querying which Users belong to a given Group requires either a single SOQL query traversing both options (with type-aware filtering) or two separate queries — one for direct User membership and one for nested Group membership, recursively expanding until all leaf Users are reached. For deeply nested group hierarchies, computing effective membership is a multi-query operation that Salesforce caches internally for performance.

Group Member rows for system-managed groups (Roles, Role-and-Subordinates, Territory) are managed by the platform, not by admins. When an admin assigns a User to a Role through Setup, Salesforce automatically maintains the corresponding Group Member rows for the Role's Public Group representations. Direct Group Member inserts on system-managed groups frequently fail validation — these groups should be modified through their owning feature (Role, Territory) rather than through Group Member directly.

Group Member is the foundation of nearly every Salesforce sharing-related feature. Public Groups, Queues, Chatter Groups, Roles (which auto-generate Public Groups), and Territory all use Group Member as their underlying membership store. Listing all the Groups a single User belongs to is a common admin troubleshooting query — SELECT Group.Name FROM GroupMember WHERE UserOrGroupId = :userId — and is often the first step in diagnosing unexpected record visibility.