Claude Henri de Rouvroy, Comte de Saint-Simon (/sænsiːˈmɒn/; French: [klod ɑ̃ʁi də ʁuvʁwa kɔ̃t də sɛ̃ simɔ̃]; 17 October 1760 – 19 May 1825), better known as Henri de Saint-Simon (French: [ɑ̃ʁi də sɛ̃ simɔ̃]), was a French political, economic and socialist theorist and businessman whose thought had a substantial influence on politics, economics, sociology and the philosophy of science. He was a younger relative of the famous memoirist the Duc de Saint-Simon.

Saint-Simon created a political and economic ideology known as Saint-Simonianism (/sænsiːˈmɒni.ənɪzəm/) that claimed that the needs of an industrial class, which he also referred to as the working class, needed to be recognized and fulfilled to have an effective society and an efficient economy. Unlike conceptions within industrializing societies of a working class being manual laborers alone, Saint-Simon's late-18th-century conception of this class included all people engaged in what he saw as productive work that contributed to society, such as businesspeople, managers, scientists, bankers, and manual labourers, amongst others.

Saint-Simon believed the primary threat to the needs of the industrial class was what he defined as the idling class: a tier of society that included able-bodied persons who, instead of using their labor to benefit the social and economic orders, preferred what he perceived as a parasitic life avoiding work. Saint-Simon stressed a three-pronged recognition of the merits of the individual, social hierarchy, and the wider economy, such as hierarchical, merit-based organizations of managers and scientists; those at the top of the hierarchies would be decision-makers in government. Saint-Simon condemned any intrusion of government into the economy beyond ensuring productive working conditions and reducing idleness in society. Saint-Simon endorsed what critics have described as authoritarian or totalitarian means to achieve his goals, saying that opponents of his proposed reforms should be "treated like cattle".

Saint-Simon's conceptual recognition of the merits of broad socioeconomic contribution and Enlightenment-era valorization of scientific knowledge inspired and influenced utopian socialism, utilitarian political theorist John Stuart Mill, anarchism (through its founder, Pierre-Joseph Proudhon), and Marxism—Karl Marx and Friedrich Engels identified Saint-Simon as an inspiration for their ideas and classified him among the utopian socialists. Saint-Simon's views also influenced 20th-century sociologist and economist Thorstein Veblen, including Veblen's influential school of institutional economics.

Henri de Saint-Simon was born in Paris as a French aristocrat, the son of Balthazar Henri de Rouvroy de Saint-Simon, Marquis de Sandricourt (1721-1783) and his wife and cousin, Blanche Isabelle de Rouvroy de Saint-Simon (b. 1737), lady-in-waiting of Marie Joséphine of Savoy, Countess of Provence. His grandfather's cousin had been the Duke of Saint-Simon. His younger sister Marie Louise de Rouvroy de Saint-Simon (1763-1834) was mother-in-law of Princess Maria Christina of Saxony, Dowager Princess of Carignano.

From his youth, Saint-Simon was highly ambitious. He ordered his valet to wake him every morning with, "Remember, monsieur le comte, that you have great things to do." Among his early schemes was one to connect the Atlantic and the Pacific oceans by a canal, and another to construct a canal from Madrid to the sea.

During the American Revolution, Saint-Simon joined the Americans, believing that their revolution signaled the beginning of a new era. He fought alongside the Marquis de Lafayette between 1779 and 1783, and took part in the siege of Yorktown under the command of General George Washington. Saint-Simon was captured and imprisoned by British forces during the end of his service, and upon his release, returned to France to study engineering and hydraulics at the Ecole de Mézières.

At the beginning of the French Revolution in 1789, Saint-Simon quickly endorsed the revolutionary ideals of liberty, equality and fraternity. In the early years of the revolution, Saint-Simon devoted himself to organizing a large industrial structure in order to found a scientific school of improvement. He needed to raise some funds to achieve his objectives, which he did by land speculation. This was only possible in the first few years of the revolution because of the growing instability of the political situation in France, which prevented him from continuing his financial activities and indeed put his life at risk. Saint-Simon and Talleyrand planned to profiteer during the Terror by buying the Cathedral of Notre-Dame, stripping its roof of metal, and selling the metal for scrap. Saint-Simon was imprisoned on suspicion of engaging in counter-revolutionary activities. He was released in 1794 at the end of the Terror. After he recovered his freedom, Saint-Simon found himself immensely rich due to currency depreciation, but his fortune was subsequently stolen by his business partner. Thenceforth he decided to devote himself to political studies and research. After the establishment of the Ecole Polytechnique in 1794, a school established to train young men in the arts of sciences and industry and funded by the state, Saint-Simon became involved with the new school.