The holdings are comprised of more than 130.000 titles and are extraordinarily valuable for the study of contemporary Spanish political history. They are divided into historical holdings and modern holdings.
Historical holdings
The historical holdings are as varied as the history of the Library, and in them certain things stand out, such as the existence of two codes from the XV century, eight incunables, fifty manuscripts from the XVI and XVII centuries, close to three hundred rare books of the same centuries, and an important collection of pamphlets from the XIX century.

Modern Holdings
The modern holdings include donations since 1943, and in them can be found specialized works of law, politics, history, social sciences, etc. The library is very complete in subjects related to the constitution, parliament, and politics, as well as being an important reference section capable of handling the high number of requests for information located there.