Fourth Reich is a rhetorical device used by political liberals in various countries, most notably Germany and the United States, to denounce their political opponents. The term is intended to convey the idea that these opponents are, in at least some degree, the ideological descendants of the Third Reich led by Adolf Hitler.

The first known uses of the term apparently focused on Neo-Nazis in Germany, often those accused of committing acts of violence against foreign — especially Turkish — guest workers. More recently, however, the term's usage has been most frequently encountered in the United States, and has been levelled by left-wing radicals either at President George W. Bush specifically, or his entire administration in general. The epithet has also been hurled at California Governor Arnold Schwarzenegger by his political opponents in that state, including representatives of the state's teachers' and nurses' unions, who are embroiled in bitter disputes with the governor; in this case the term has a double meaning, in that Schwarzenegger's father was a minor Nazi Party official in the governor's native Austria.