Friedenstein Palace (German: Schloss Friedenstein) is an early Baroque palace in the city of Gotha, built in the mid-17th century by Ernest I, Duke of Saxe-Gotha at Gotha, Thuringia, Germany. In Germany, Friedenstein was one of the largest palaces of its time and one of the first Baroque palaces ever built. Friedenstein served as the main seat of the Dukes of Saxe-Gotha and later as one of the residences of the Dukes of Saxe-Coburg and Gotha, closely linked with the royal family of Great Britain through the marriage of Queen Victoria and Prince Albert. The final two ruling Dukes were both princes of the United Kingdom.

The palace complex today houses several museums. It is also notable for hosting the Ekhof-Theater [de], one of the oldest theatres in operation in Germany, still featuring the original Baroque machinery for changing the scenery.

The site where Friedenstein stands today, dominating the town of Gotha and its surroundings, was previously occupied by Grimmenstein Castle. It was first mentioned in 1316 and rebuilt in 1531-43 when it was also fortified in accordance with the changed requirements for a fortress in the age of gunpowder. In 1547, the Ernestine branch of the House of Wettin as members of the Protestant Schmalkaldic League had lost the Battle of Mühlberg against the Catholic forces of Emperor Charles V. As a result, Johann Friedrich I, Kurfürst von Sachsen (John Frederick I) was stripped of his title as "Elector of Saxony" (Kurwürde). Imperial forces blew up the fortifications of Grimmenstein but left the castle itself largely intact. It was rebuilt in 1552-54. However, in 1567 the fortress was almost completely razed as a result of the attempt of Johann Friedrich II (John Frederick II) to regain the Kurwürde by force of arms.

In 1640, Ernest I, Duke of Saxe-Gotha, also known as Ernst der Fromme ("Ernest the Pious"), first ruler of the newly created Duchy of Saxe-Gotha, settled on Gotha as the site for his Residenz. Gotha at the time was the largest town in the Duchy. In 1641/42 work began on the park, followed by construction of the palace itself in 1643. In naming the castle Friedenstein (literally "peace-rock"), Ernst made a point of drawing a clear line between this new palace and the warlike history of its predecessor. In addition, with the Thirty Years War still ongoing, the name also expressed a desire for peace after decades of warfare.

Based on plans by Casper Vogell [de] (1600-1663), Andreas Rudolph [de] (1601-1679) was in charge of building the castle. When it was finished in 1656, Friedenstein was the first ever Residenz in the Baroque style built on German soil that was completed during the lifetime of the ruler who ordered it. To justify the expense of such a vast structure, Ernest explicitly referred to the need to accommodate the administration for the new Duchy.

In July 1655, work began on fortifying the castle. By 1672, four bastions had been completed. The outer works were finished by 1687 and, beginning in 1663, the town of Gotha was also fortified. In 1672, the House of Saxe-Altenburg ended and most of the Duchy passed to Ernst, who now was ruler of Saxe-Gotha-Altenburg. Although the Duchy now had two Residenzen, Gotha was by far the more important one.

However, Ernst was unwilling to exclude any of his surviving sons from his heritage. So after his death in 1675, the Duchy was split in 1680/81 into seven separate territories: Saxe-Gotha-Altenburg, Saxe-Coburg, Saxe-Meiningen, Saxe-Römhild, Saxe-Eisenberg, Saxe-Hildburghausen and Saxe-Saalfeld. Ernst's oldest son, Friedrich I, became Duke of Saxe-Gotha-Altenburg, with his main Residenz at Gotha.

In 1826, after the death of the heirless Friedrich IV, the Duchy was split and Gotha passed to Ernst I of the House of Saxe-Coburg and father of Albert, Prince Consort who was to marry Queen Victoria. Ernst I now styled himself "Duke of Saxe-Coburg and Gotha", although he technically held the two separate Duchies of Saxe-Coburg and Gotha in personal union.