The Reign of Terror (French: la Terreur) was a period of the French Revolution when, following the creation of the First Republic, a series of massacres and numerous public executions took place in response to revolutionary fervour, anticlerical sentiment, and accusations of treason by the Committee of Public Safety.

There is disagreement among historians over when exactly "the Terror" began. Some consider it to have begun only in 1793, giving the date as either 5 September, June or March, when the Revolutionary Tribunal came into existence. Others, however, cite the earlier time of the September Massacres in 1792, or even July 1789, when the first killing of the revolution occurred.

The term "Terror" being used to describe the period was introduced by the Thermidorian Reaction who took power after the fall of Maximilien Robespierre in July 1794, to discredit Robespierre and justify their actions. Today there is consensus amongst historians that the exceptional revolutionary measures continued after the death of Robespierre, and this subsequent period is now called the "White Terror". By then, 16,594 official death sentences had been dispensed throughout France since June 1793, of which 2,639 were in Paris alone; and an additional 10,000 died in prison, without trial, or under both of these circumstances.