Louis XVI (Louis-Auguste; French pronunciation: ​[lwi sɛːz]; 23 August 1754 – 21 January 1793) was the last King of France before the fall of the monarchy during the French Revolution. He was referred to as Citizen Louis Capet during the four months just before he was executed by guillotine. He was the son of Louis, Dauphin of France, son and heir-apparent of King Louis XV, and Maria Josepha of Saxony. When his father died in 1765, he became the new Dauphin. Upon his grandfather's death on 10 May 1774, he assumed the title King of France and Navarre until 4 September 1791, when he received the title of King of the French until the monarchy was abolished on 21 September 1792.

The first part of his reign was marked by attempts to reform the French government in accordance with Enlightenment ideas. These included efforts to abolish serfdom, remove the taille (land tax) and the corvée (labour tax), and increase tolerance toward non-Catholics as well as abolish the death penalty for deserters. The French nobility reacted to the proposed reforms with hostility, and successfully opposed their implementation. Louis implemented deregulation of the grain market, advocated by his economic liberal minister Turgot, but it resulted in an increase in bread prices. In periods of bad harvests, it led to food scarcity which, during a particularly bad harvest in 1775, prompted the masses to revolt. From 1776, Louis XVI actively supported the North American colonists, who were seeking their independence from Great Britain, which was realised in the 1783 Treaty of Paris. The ensuing debt and financial crisis contributed to the unpopularity of the Ancien Régime. This led to the convening of the Estates-General of 1789. Discontent among the members of France's middle and lower classes resulted in strengthened opposition to the French aristocracy and to the absolute monarchy, of which Louis and his wife Queen Marie Antoinette were viewed as representatives. Increasing tensions and violence were marked by events such as the storming of the Bastille, during which riots in Paris forced Louis to definitively recognize the legislative authority of the National Assembly.

Louis's indecisiveness and conservatism led some elements of the people of France to view him as a symbol of the perceived tyranny of the Ancien Régime, and his popularity deteriorated progressively. His unsuccessful flight to Varennes in June 1791, four months before the constitutional monarchy was declared, seemed to justify the rumors that the king tied his hopes of political salvation to the prospects of foreign intervention. The credibility of the king was deeply undermined, and the abolition of the monarchy and the establishment of a republic became an ever-increasing possibility. The growth of anti-clericalism among revolutionaries resulted in the abolition of the dîme (religious land tax) and several government policies aimed at the dechristianization of France.

In a context of civil and international war, Louis XVI was suspended and arrested at the time of the Insurrection of 10 August 1792. One month later, the monarchy was abolished and the First French Republic was proclaimed on 21 September 1792. Louis was then tried by the National Convention (self-instituted as a tribunal for the occasion), found guilty of high treason and executed by guillotine on 21 January 1793, as a desacralized French citizen under the name of Citizen Louis Capet, in reference to Hugh Capet, the founder of the Capetian dynasty – which the revolutionaries interpreted as Louis's surname. Louis XVI was the only king of France ever to be executed, and his death brought an end to more than a thousand years of continuous French monarchy. Both of his sons died in childhood, before the Bourbon Restoration; his only child to reach adulthood, Marie Thérèse, was given over to the Austrians in exchange for French prisoners of war, eventually dying childless in 1851.