The Załuski brothers' greatest passion was books. Józef Andrzej Załuski and his brother Andrzej Stanisław Załuski acquired the collections of earlier Polish bibliophiles such as Jakub Zadzik, Krzysztof Opaliński, Tomasz Ujejski, Janusz Wiśniowiecki, Jerzy Mniszech and Jan III Sobieski. From the 1730s the brothers planned the creation of a library, and in 1747 they founded the Załuski Library. Located in the 17th-century Daniłowicz Palace in Warsaw, the library building had two stories and was topped with a small tower containing an astronomical observatory. The building's reconstruction in rococo style was accomplished in 1745 by Francesco Antonio Melana and his brother. The Załuski Library was considered the first Polish public library and one of the largest libraries in the contemporary world. In all of Europe there were only two or three libraries that could boast such holdings. The library initially held some 200,000 items, which grew to some 400,000 printed items, maps and manuscripts by the end of the 1780s. It also accumulated a collection of art, scientific instruments, and plant and animal specimens. This library, open on Tuesdays and Thursdays from 7:00 a.m. to 7:00 p.m., asked patrons to be quiet and to say a prayer in the intention of the Załuski brothers. It was prohibited to take the books outside the library, as the book theft was a growing problem, to an extent that the bishop patrons decided to ask the pope for help. Responding to their request, in 1752 pope Benedict XIV issued a papal bull that threatened to excommunication individuals taking the books from this library; even that did not eliminate the problem completely.
After the brothers' deaths, the newly formed Commission for National Education took charge of the library, renaming it the Załuski Brothers' Library of the Republic. Twenty years later in 1794, in the aftermath of the second Partition of Poland and Kościuszko Uprising, Russian troops, on orders from Russian Czarina Catherine II, emptied the library and dispatched the whole collection to Saint Petersburg, where the books formed the mass of the Imperial Public Library on its formation, a year later. Parts of the collections were damaged or destroyed as they were mishandled while being removed from the library and transported to Russia, and many were stolen. According to the historian Joachim Lelewel, the Zaluskis' books, "could be bought at Grodno by the basket". The collection was later dispersed among several Russian libraries. Some parts of the Zaluski collection came back to Poland on two separate dates in the nineteenth century: 1842 and 1863. In the 1920s, in the aftermath of the Polish-Soviet War and the Treaty of Riga the RSFSR's government returned around 50,000 items from the collection to Poland, yet German soldiers deliberately destroyed these items during the Planned destruction of Warsaw in October 1944, after collapse of the Warsaw Uprising. Only 1800 manuscripts and 30,000 printed materials from the original library survived the war. In 1821 the library's original home was altered into a tenement house. During the building's reconstruction, the busts of Polish monarchs that had originally adorned the library's interiors, and which had been hidden during the Partitions of Poland, were discovered and placed on the building's facade; hence the building came to be called the "House of the Kings". The building was destroyed by the Germans during World War II. After the war, it was rebuilt under the Polish People's Republic. Today's Polish National Library, founded in 1928, considers itself the descendant of the Załuski Library.
