The holdings, divided into the historical and modern divisions, comprise more than 500.000 titles and are extraordinarily valuable for the study of contemporary Spanish political history.

Historical holdings
The historical holdings are as varied as the history of the library, including for instance and to name only a few two codes from the XV century, eight incunabula, fifty manuscripts from the XVI and XVII centuries, around three hundred rare books of the said centuries, and a remarkable collection of pamphlets from the XIX century.

Modern holdings
The modern holdings are those acquired since 1943 to date, and include many specialized works on law, politics, history, social sciences and the like. Special attention is paid to subjects related to the constitutional and parliamentary law, public and administrative law, and politics.