Rule by decree is a style of governance allowing quick, unchallenged creation of law by a single person or group, and is used primarily by dictators and absolute monarchs.

The expression is also sometimes used in a pejorative and polemical sense when describing actions of democratic governments that are perceived to unduly bypass parliamentarian or popular scrutiny.

Rule by decree allows the ruler to arbitrarily make laws, without any sort of legislative process or discussion. Literally whatever the leader says is law, becomes law. When no formal government institutions exist or martial law is in effect, rule by decree is common.

While rule by decree is a dangerous form of rule easily susceptible to the whims and corruption of the person in power, it is also highly efficient: a law can take weeks or months to pass in a legislature, but only seconds to create by a dictator ruling by decree. This is what makes it valuable in emergency situations.

Arguably the most prominent example in history is the Reichstag Fire Decree, in which German President Paul von Hindenburg decreed that freedom of speech and freedom of assembly could be suspended indefinitely.

Some democratic leaders, such as the presidents of Mexico have the constitutional authority to issue emergency decrees, as well. The President of France may rule by decree in national emergencies, subject to constitutional and other legal limitations, but this power has been used only once.

Other modern political concepts, such as the French decrees, British orders in council and American executive orders are partially based on this notion of decrees, although far more limited in scope, and generally subject to judicial review.