The Radziwiłł Collection of the National Library of Finland consists of a part of the Nesvizh Castle Library of the Polish-Lithuanian royal family of Radziwiłł. The Radziwiłł royal family was a significant family in the region of Poland and Lithuania since the 15th century. The family collected a notable library for its Nesvizh Castle. In 1772, the library was transferred to the Saint Petersburg Academy of Sciences, and part of it, over 1,200 works, was donated to Helsinki in 1829.
The Radziwiłł library and archives were included in the UNESCO's Memory of the World register in 2009. In addition to Helsinki, parts of the Radziwiłł library are located in 9 different European libraries.
In Helsinki, the books from the collection were originally integrated into various sub-collections. Thus far, about 900 of them have been recognised.