Nicolas-Claude Fabri de Peiresc (1 December 1580 – 24 June 1637), often known simply as Peiresc, or by the Latin form of his name, Peirescius, was a French astronomer, antiquary and savant, who maintained a wide correspondence with scientists, and was a successful organizer of scientific inquiry.

His research included a determination of the difference in longitude of various locations in Europe, around the Mediterranean, and in North Africa.

He is notably known for having been Galileo’s lawyer, a close friend of Rubens, an art advisor to Marie de' Medici, a pioneer of Egyptology, and for undertaking the first map of the Moon based on telescopic observations. Marc Fumaroli described him as the prince of the Republic of Letters.

Peiresc's father was a higher magistrate and city surgeon in Provence from a wealthy noble family, who with his wife fled their home town of Aix-en-Provence to avoid the plague raging there, settling in Belgentier in Var. Peiresc was born in Belgentier and educated in Aix-en-Provence and Avignon, as well as at the Jesuit college at Tournon. At Toulon, he first became interested in astronomy. Studying law and becoming interested in archaeology, he travelled to Italy, Switzerland and France in 1599, and finally finished his legal studies in 1604 at the University of Montpellier. It was also in 1604 that he assumed the name Peiresc after a domain in Alpes-de-Haute-Provence (now spelled Peyresq) which he had inherited from his father, although he himself never visited it.

After receiving his degree, he travelled to Paris (in 1605–1606, with his patron Guillaume du Vair, president of the Parlement of Provence), London and Flanders before returning to Aix in 1607 to take over his uncle's position as conseiller in the Parlement of Provence under du Vair. He held this post until 1615.

From 1615 until 1622, Peiresc again visited Paris with du Vair. He then returned to Provence to serve as senator of the sovereign court. He became a patron of science and art, studied fossils, and supported the astronomer Pierre Gassendi from 1634 to 1637. Virginio Cesarini proposed him for membership of the Accademia dei Lincei in 1621, but it is not certain whether he joined.

Peiresc's position as a great intellectual at the time of the Scientific Revolution has led to his being called a "Prince of the Republic of Letters". He was also a noted politician in his home region, and a tireless letter-writer (10,000 of his letters survive, and he was in constant correspondence with François de Malherbe, Hugo Grotius, the brothers Dupuy, Alphonse-Louis du Plessis de Richelieu, and with his great friend Rubens. His correspondence to Malherbe throws light on the personality of Malherbe's troubled son Marc-Antoine Malherbe.

Peiresc became one of the first admirers and supporters of Caravaggio in France. He first discovered Caravaggio's works in the Contarelli chapel in Rome in 1600 when he was only 20 years old. In his hometown, he gathered around him a sort of 'caravaggesque workshop of Southern France' with artists including Flemish artist Louis Finson, Martin Hermann Faber, Trophime Bigot and other painters. He promoted the Caravaggesque style by arranging commissions for these artists. He was instrumental in obtaining a number of commissions for Finson, including for history paintings and portraits. Finson also painted a portrait of de Peyresc. Peiresc was an avid art collector and relied on Finson's contacts in Italy to acquire two works of Caravaggio from the Pasqualini family of Rome.