Cyril and Methodius National Library and keeps more than 1.5 million documents and a separate collection "Portraits and Photos" consisting of 80,000 photos all of historical importance for Bulgaria and the Balkans.
The archive is one of the earliest historical document repositories in Bulgaria.
It was established in 1878, just after the Bulgarian Liberation and was then known as the Archives Department of the library.
The greatest number of documents come from the period middle 19th century to middle 20th century representing the Bulgarian National Revival and post-Liberation period of Bulgarian history.
Also covered in great detail are the Bulgarian liberation struggles in Macedonia and the Odrin region after the Liberation.