The holdings of the Gotha Research Library include 93 bequests from the 16th to the 20th century. Among them are letters, notes, drawings – in other words, written materials from phases of literary and scientific production by personalities of very different professional persuasions. These include authors, researchers, librarians, cartographers, a singer, botanists, agriculturists, theologians, architects, classical philologists, philosophers, orientalists, lawyers, astronomers and pedagogues, as well as polymaths or polyhistorians, dukes, teachers, local historians, doctors and painters.
The collection includes, for example, the bequests of the botanists Jakob (1637–1697) and Johann Philipp Breyne (1680-1764), the theologian and Gotha Superintendent General Carl Gottlieb Bretschneider (1776–1846) as well as the theologian Johann Gerhard (1582–1637), who was important for Lutheran orthodoxy, and his son Johann Ernst Gerhard (1621–1668), a Lutheran theologian and early orientalist. The estate of the astronomer Peter Andreas Hansen (1795–1874), who worked as director of the Gotha Ducal Observatory, is also kept in the research library.
There are also documents from numerous personalities who left their mark on cultural life in Gotha and beyond, such as the estate of the Gotha natural scientist and author Kurd Lasswitz (1848–1910) and the Gotha painter and graphic artist Franz Vetter (1886–1967). The latter compiled a Hermann Hesse collection during more than 50 years of correspondence with the poet and author. The partial estate of the Gotha-born publicist and publisher Joseph Kürschner (1853–1902; correspondence with Henrik Ibsen, Karl May and Wilhelm Raabe and others), who was internationally known, is also kept in the research library.
The research library also houses the estates of important dukes, including Bernhard, Duke of Saxe-Weimar (1604–1639), Ernest II, Duke of Saxe-Gotha-Altenburg (1745–1804), and August, Duke of Saxe-Gotha-Altenburg (1772–1822).