Cosimo II de' Medici (12 May 1590 – 28 February 1621) was Grand Duke of Tuscany from 1609 until his death. He was the elder son of Ferdinando I de' Medici, Grand Duke of Tuscany, and Christina of Lorraine.

For the majority of his twelve-year reign, he delegated the administration of Tuscany to his ministers. He is best remembered as the patron of Galileo Galilei, his childhood tutor.^[1]

Cosimo's father Ferdinando I took care to provide him with a modern education. Indeed, Galileo Galilei was Cosimo's tutor between 1605 and 1608. Ferdinando arranged for him to marry Archduchess Maria Maddalena of Austria, daughter of Archduke Charles II, in 1608. Together they had eight children, among whom was Cosimo's eventual successor, Ferdinando II, an Archduchess of Inner Austria, a Duchess of Parma and two cardinals.

Ferdinando I died in 1609. Due to his precarious health, Cosimo did not actively participate in governing his realm, but he was a great patron of science and letters. Just over a year after Cosimo's accession, Galileo dedicated his Sidereus Nuncius, an account of his telescopic discoveries, to the grand duke.^[2]

In spite of his lack of interest in governance, the grand duke did assiduously enlarge the navy.

He died on 28 February 1621 from tuberculosis and was succeeded by his elder son, Ferdinando II, still a minor at the time of his father's death. The regency for the new grand duke was bestowed upon Cosimo II's wife and mother, as per his wishes.

Galileo Galilei was named court mathematician to Cosimo in 1610, a post that freed Galileo from the constraints of teaching mathematics at universities. As court mathematician, Galileo was free to challenge the distinction between disciplines and advance theories of Nicolaus Copernicus by using mathematics to address questions of physics.^[3] The already famous Galileo had used his telescopic accomplishments in his bid for patronage. Once appointed, Galileo moved to the Florence court and found a resource rich environment where he worked as philosopher, mathematician^[4] and astronomer.^[5] Galileo was actively involved in court life and supported the dynastic rhetoric of the Medici family. Aside from producing intellectual spectacles, Galileo used the Medici court to advance his theoretical claims and discoveries. The four moons of Jupiter he had discovered were named Medicean Stars in reference to Cosimo and his three brothers. Tuscan ambassadors were used to advance scientific debate in Europe. Ambassadors in Prague, Paris, London and Madrid received copies of Galileo's Sidereus Nuncius and were sent telescopes constructed by Galileo, paid for by the court treasury.^[6]