The collection of correspondence of Hüseyin Hilmi Pasha, who was the Grand Vizier at the time of the March 31st Incident, is an important source for researchers interested in late Ottoman history, the Committee of Union and Progress, the Balkans and Macedonia. Hüseyin Hilmi Pasha's official and personal correspondence is an important primary source for national and international political developments in the Balkans, especially during his Rumelia Inspectorate. The documents from this inspectorate period account for more than half of the collection.

Rıza Tevfik Bölükbaşı (1869-1949), known as “Feylesof” (philosopher) was a poet, literary figure, politician, and philosopher of the Second Constitutional Monarchy period. He studied medicine, served as a member of parliament during the Ottoman period, and lived in exile for many years, as he was among the “Hundred and Fifty” of the Ottoman delegate who signed the Treaty of Sevres.
The collection spans the period between 1856 and 1997 and has been categorized in 32 folders and 925 separate files. Consisting primarily of correspondence with prominent people and institutions in Turkey and around the world, as well as manuscripts, photographs, and newspaper clippings, the collection contains 12,978 pages and 3,998 documents. This represents an important source for the last period of the Ottoman Empire and the early years of the Republic.