In politics of the United States, the fourth branch of government is an unofficial term referring to groups or institutions perceived variously as influencing or acting in the stead of the three branches of the US federal government defined in the Constitution of the United States (legislative, executive and judicial). Views as to whether the influence is due or undue or the actions are for good or ill also vary.

Such groups can include the press (as a departure from the 'Fourth Estate'), the people (in sum or as grand juries), and interest groups. The independent administrative agencies of the United States government, while technically part of any one of the three branches, may also be referred to as a ‘fourth branch’.