Gian Gastone de' Medici (Giovanni Battista Gastone; 24 May 1671 – 9 July 1737) was the seventh and last Medicean Grand Duke of Tuscany.
He was the second son of Grand Duke Cosimo III and Marguerite Louise d'Orléans. His sister, Electress Palatine Anna Maria Luisa, arranged his marriage to the wealthy and widowed Anna Maria Franziska of Saxe-Lauenburg in 1697. The couple despised each other and had no children. As Grand Prince Ferdinando, Gian Gastone's elder brother, predeceased Cosimo III, Gian Gastone succeeded his father in 1723.
His reign was marked by the reversal of his predecessor's conservative policy; he abolished taxes for poorer people, repealed penal laws which restricted Jews and discontinued public executions. The Medici were wanting in male heirs; his father, Cosimo III, wanted the Electress Palatine to succeed Gian Gastone. However, Spain, Great Britain, Austria and the Dutch Republic disregarded Cosimo's plan and appointed Charles of Spain—whose mother, Elisabeth Farnese, was a great-granddaughter of Margherita de' Medici—Gian Gastone's heir. Charles later transferred his claim to Francis Stephen of Lorraine pursuant to a preliminary peace that was finalized in 1738. Francis Stephen duly succeeded at Gian Gastone's demise, on 9 July 1737, ending almost 300 years of Medici rule over Florence. For the latter part of his reign, Gian Gastone chose to remain confined in his bed, tended by his entourage, the Ruspanti.