Claude-Nicolas Ledoux (French pronunciation: [klod nikɔla lədu]; 21 March 1736 – 18 November 1806) was one of the earliest exponents of French Neoclassical architecture. He used his knowledge of architectural theory to design not only domestic architecture but also town planning; as a consequence of his visionary plan for the Ideal City of Chaux, he became known as a utopian. His greatest works were funded by the French monarchy and came to be perceived as symbols of the ancien régime rather than Utopia. The French Revolution hampered his career; much of his work was destroyed in the nineteenth century. In 1804, he published a collection of his designs under the title L'Architecture considérée sous le rapport de l'art, des mœurs et de la législation (Architecture considered in relation to art, morals, and legislation). In this book he took the opportunity of revising his earlier designs, making them more rigorously neoclassical and up to date. This revision has distorted an accurate assessment of his role in the evolution of Neoclassical architecture. His most ambitious work was the uncompleted Royal Saltworks at Arc-et-Senans, an idealistic and visionary town showing many examples of architecture parlante. Conversely his works and commissions also included the more mundane and everyday architecture such as approximately sixty elaborate tollgates around Paris in the Wall of the General Tax Farm.

Ledoux was born in 1736 in Dormans-sur-Marne, the son of a modest merchant from Champagne. At an early age his mother, Francoise Domino, and godmother, Francoise Piloy, encouraged him to develop his drawing skills. Later the Abbey of Sassenage funded his studies in Paris (1749–1753) at the Collège de Beauvais, where he followed a course in Classics. On leaving the Collège, age 17, he took employment as an engraver but four years later he began to study architecture under the tutelage of Jacques-François Blondel, for whom he maintained a lifelong respect.

He then trained under Pierre Contant d'Ivry, and also made the acquaintance of Jean-Michel Chevotet. These two eminent Parisian architects designed in both the restrained French Rococo manner, known as the "Louis XV style" and in the "Goût grec" (literally "Greek taste") phase of early Neoclassicism. However, under the tutelage of Contant d'Ivry and Chevotet, Ledoux was also introduced to Classical architecture, in particular the temples of Paestum, which, along with the works of Palladio, were to influence him greatly.

The two master architects introduced Ledoux to their affluent clientele. One of Ledoux's first patrons was the Baron Crozat de Thiers, an immensely wealthy connoisseur who commissioned him to remodel part of his palatial town house in the Place Vendôme. Another client obtained through the auspices of his teachers was Président Hocquart de Montfermeil and his sister, Mme de Montesquiou.

In 1762, the young Ledoux was commissioned to redecorate the Café Godeau, in the rue Saint-Honoré. The result was an interior of trompe-l'œil and mirrors. Pilasters painted on the walls were interspersed with alternating Pier glasses and panels painted with trophies of helmets and weaponry, all executed in bold detail. In 1969 this interior was moved to the Musée Carnavalet.

The following year the Marquis de Montesquiou-Fézensac commissioned Ledoux to redesign the old hilltop château on his estate at Mauperthuis. Ledoux rebuilt the château and created new gardens, replete with fountains supplied by an aqueduct. In addition in the gardens and park he built an orangery, a pheasantry and vast dépendances of which little remains today.

In 1764, he designed for Président Hocquart, a Palladian house on the Chaussée d'Antin using the colossal order. Ledoux would frequently employ this motif that was condemned by the strict French tradition, which embraced the principle of superimposing the classic column motifs on each floor, rising from simplest to the most complex: Tuscan, Doric, Ionic, Corinthian, etc.

On 26 July 1764, in the Saint-Eustache Church, Paris, Ledoux married Marie Bureau, the daughter of a court musician. A friend from Champagne, Joseph Marin Masson de Courcelles, found him a position as the architect for the Water and Forestry Department. Here between 1764 and 1770 he worked on the renovation and designs of churches, bridges, wells, fountains and schools.