Following the definition applied to archives, personal collection is understood as “the set of documents, whatever their date, form or medium, generated, received and grouped by a person in the performance of their professional and personal activities throughout their life.” The National Library of Spain holds around a hundred personal archives of prominent figures in the fields of literature, politics and music, whose formation has been contributed to by the institution's gradual interest in these sources of information that are invisible until an organisation makes them public. The variety and richness of the documents they contain make them essential sources of information for research.