The 'Engraved Royal Portrait' (ERP) series contains over 22,000 prints, in all techniques. As most of the prints reproduce painted portraits, they constitute a comprehensive survey of the portraiture of the monarchies of European nations. The ERP series has been added to continuously over the last three centuries, and the resulting collection is now the largest group of works on paper in the Royal Collection.

The ERPs are arranged by nationally, dynasty, and sitter over the course of 66 volumes and 30 portfolios, housed in the Print Room at Windsor Castle. The largest single section, numbering over 7,000 prints, contains British monarchs from the early Anglo-Saxon kings and legendary Scottish rulers through to Queen Elizabeth II, spanning five centuries of printmaking. The majority of the ERPs were bound into large volumes in the early twentieth century under the librarian Sir John Fortescue; many others which were subsequently added or not bound into volumes have remained in portfolios.