State terrorism is terrorism conducted by a state against its own citizens or another state's citizens. It contrasts with state-sponsored terrorism, in which a violent non-state actor conducts an act of terror under sponsorship of a state.

Governments accused of state terrorism may justify these actions as efforts to combat internal dissent, suppress insurgencies, or maintain national security, often framing their actions within the context of counterterrorism or counterinsurgency. Accused actions of state terrorism are normally also criticised as severe violations of human rights and international law.

Historically, governments have been accused of using state terrorism in various settings. The exact definition and scope of state terrorism remain controversial, as some scholars and governments argue that terrorism is a tool used exclusively by non-state actors, while others maintain that state-directed violence intended to terrorize civilian populations should also be classified as terrorism.

There is neither an academic nor an international legal consensus regarding the proper definition of the word terrorism. Some scholars believe the actions of governments can be labelled "terrorism". Using the term 'terrorism' to mean violent action used with the predominant intention of causing terror, Paul James and Jonathan Friedman distinguish between state terrorism against non-combatants and state terrorism against combatants, including "shock and awe" tactics:

"Shock and Awe" as a subcategory of "rapid dominance" is the name given to massive intervention designed to strike terror into the minds of the enemy. It is a form of state-terrorism. The concept was however developed long before the Second Gulf War by Harlan Ullman as chair of a forum of retired military personnel.

However, others, including governments, international organisations, private institutions and scholars, believe the term terrorism is applicable only to the actions of violent non-state actors. This approach is termed as an actor-centric definition which emphasizes the characteristics of the groups or individuals who use terrorism; whilst act-centric definitions emphasize the unique aspects of terrorism from other acts of violence. Historically, the term terrorism was used to refer to actions taken by governments against their own citizens whereas now it is more often perceived as targeting of non-combatants as part of a strategy directed against governments.

Historian Henry Commager wrote that "Even when definitions of terrorism allow for 'state terrorism', state actions in this area tend to be seen through the prism of war or national self-defense, not terror." Most states use the term terrorism for non-state actors only.

The Encyclopædia Britannica Online defines terrorism generally as "the systematic use of violence to create a general climate of fear in a population and thereby to bring about a particular political objective", and states that "terrorism is not legally defined in all jurisdictions". The encyclopedia adds that "[e]stablishment terrorism, often called state or state-sponsored terrorism, is employed by governments—or more often by factions within governments—against that government's citizens, against factions within the government, or against foreign governments or groups."