Carl Philipp Gottlieb von Clausewitz (pronounced /ˈklaʊzəvɪts/; July 1, 1780 – November 16, 1831) was a Prussian soldier, military historian and military theorist. He is most famous for his military treatise Vom Kriege, translated into English as On War.

Clausewitz, considered an author of contemporary military strategy, was born in Burg bei Magdeburg, Kingdom of Prussia, to a poor but middle-class family. His grandfather, the son of a Lutheran Pastor, had been a professor of theology. Clausewitz's father was once a lieutenant in the Prussian army and held a minor post in the Prussian internal revenue service. Carl was the fourth and youngest son. He entered the Prussian military service at the age of twelve years as a Lance-Corporal, eventually attaining the rank of Major-General.

Clausewitz served in the Rhine Campaigns (1793–1794) e.g. the Siege of Mainz, when the Prussian army invaded France during the French Revolution, and later served in the Napoleonic Wars from 1806 to 1815. Clausewitz entered the Kriegsakademie in Berlin (also cited variously as "The German War School," the "Military Academy in Berlin," and the "Prussian Military Academy") in 1801 (age 21 years), studied the writings of the philosopher Immanuel Kant, and won the regard of General Gerhard von Scharnhorst, the future first chief of staff of the new Prussian Army (appointed 1809). Clausewitz, along with Hermann von Boyen (1771–1848) and Karl von Grolman (1777–1843), were Scharnhorst's primary allies in his efforts to reform the Prussian army, between 1807 and 1814.