The Church of the Grand Duchy of Lithuania’s Uniates or Catholics of the Greek Rite was established in 1596 and abolished in 1839. Documents, namely manuscripts, letters, printed books, plans of land possessions, images, photos etc., reveal the historical destiny of the Uniates and their activities in the various areas of life. The development and destiny of the Uniate Church is closely related to the Order of Basil the Great or the Basilians (operated between 1617 and 1839). Documents covering educational and cultural activities of the Basilians comprise a significant part of the Grand Duchy of Lithuania’s heritage.