Members of the French National Guard under the command of General Lafayette open fire on a crowd of radical Jacobins at the Champ de Mars, Paris, during the French Revolution, killing scores of people.

The Champ de Mars massacre took place on 17 July 1791 in Paris at the Champ de Mars against a crowd of republican protesters amid the French Revolution. Two days before, the National Constituent Assembly issued a decree that King Louis XVI would retain his throne under a constitutional monarchy. This decision came after Louis and his family had unsuccessfully tried to flee France in the Flight to Varennes the month before. Later that day, leaders of the republicans in France rallied against this decision.

Jacques Pierre Brissot was the editor and main writer of Le Patriote franais and president of the Comit des Recherches of Paris, and he drew up a petition demanding the removal of the king. A crowd of 50,000 people gathered at the Champ de Mars on 17 July to sign the petition, and about 6,000 signed it. However, two suspicious people had been found hiding at the Champ de Mars earlier that day, "possibly with the intention of getting a better view of the ladies' ankles"; they were hanged by those who found them, and Paris Mayor Jean Sylvain Bailly used this incident to declare martial law. Lafayette and the National Guard under his command were able to disperse the crowd.

Georges Danton and Camille Desmoulins led the crowd, and they returned in even higher numbers that afternoon. The larger crowd was also more determined than the first, and Lafayette again tried to disperse it. In retaliation, they threw stones at the National Guard. After firing unsuccessful warning shots, the National Guard opened fire directly on the crowd. The exact numbers of dead and wounded are unknown; estimates range from a dozen to 50 dead.

The National Guard (French: Garde nationale) is a French military, gendarmerie, and police reserve force, active in its current form since 2016 but originally founded in 1789 during the French Revolution.

For most of its history the National Guard, particularly its officers, has been widely viewed as loyal to middle-class interests.

It was founded as separate from the French Army and existed both for policing and as a military reserve. However, in its original stages from 1792 to 1795, the National Guard was perceived as revolutionary and the lower ranks were identified with sans-culottes. It experienced a period of official dissolution from 1827 to 1830 but was reestablished. Soon after the Franco-Prussian War of 1870–71, the National Guard in Paris again became viewed as dangerously revolutionary, which contributed to its dissolution in 1871.In 2016, France announced the reestablishment of the National Guard for the second time, in response to a series of terrorist attacks in the country.