Ex rel.

The abbreviation ex rel. stands for the Latin phrase ex relatione. Ex relatione is a procedural phrase in the Bluebook, meaning "on the relation of", “out of the relation of”, or “on behalf of.”  This is a phrase showing that the plaintiff is suing based on information from another person. In the case caption, the party named after "ex rel." is the party on whose information the suit is brought, this party is called the relator.  Many government lawsuits based on whistleblowers' information are brought as suits ex rel.