Palatinal Crypt in the context of Royal Palace (Budapest)

The National Széchényi Library (Hungarian: Országos Széchényi Könyvtár, pronounced [ˈorsaːɡoʃ ˈseːt͡ʃeːɲi ˈkøɲftaːr]) (OSZK) is a library in Budapest, Hungary, located in Buda Castle. It is one of the two Hungarian national libraries, the other being University of Debrecen Library.

Buda Castle (Hungarian: Budavári Palota, German: Burgpalast), formerly also called the Royal Palace (Hungarian: Királyi-palota) and the Royal Castle (Hungarian: Királyi Vár, German: Königliche Burg), is the historical castle and palace complex of the Hungarian kings in Budapest. First completed in 1265, the Baroque palace that occupies most of the site today was built between 1749 and 1769, severely damaged during the Siege of Budapest in World War II, and rebuilt in a simplified Baroque style during the state communist era. Presently, it houses the Hungarian National Gallery, the Budapest Historical Museum, and the National Széchényi Library.

The palace complex sits on the southern tip of Castle Hill (Hungarian: Várhegy). Its defensive walls extend to surround the entire Castle Quarter (Várnegyed) neighborhood to its north, which is well known for its medieval, Baroque, and neoclassical houses, churches, and other monuments. Several prominent government buildings, including Sándor Palace and the Carmelite Monastery of Buda, are located in the Castle Quarter. Locally, this neighborhood and the palace are collectively called a Vár (lit. 'the Castle').