As a scientist, Šišić was primarily interested in the history of the early and high Middle Ages in Croatia. His greatest work is History of the Croats Under Home Rule, while his most popular work is Overview of the History of the Croatian People, which was edited by Jaroslav Šidak and widely used for almost five decades. History of the Croats under the Arpad Kings, an unfinished compilation published after his death, is generally considered below the level of his magnum opus. Other notable Šišić's books are the important monograph on Hrvoje Vukčić Hrvatinić and a critical edition of Dukljanin's Chronicles. His compilations of Croatian history of later periods are not as valuable as his epochal history of the Croatian early Middle Ages. The work of Ferdo Šišić is characterized by a systematic, objective and informed approach. His opus, however, is the high point of "genetic history" or the archivist's approach, which patiently weaves the tapestry of the chosen period without engaging in speculations that are sometimes necessary to fill the gaps left open by archive materials. Also, the Croatian historiography came to be dominated by the multidisciplinary approach combining demographics, culturology, history of economy and art only in the second half of the 20th century, putting Šišić in the position of a classic who laid inestimable foundations but cannot be the role model for contemporary historical science.
Politician and archivist
Šišić was politically engaged as a member of the Croato-Serbian Coalition from 1908 to 1917. His biographers sometimes talk about Šišić's political inconstancy, material ambitions, weak character and opportunism. But Šišić is neither interesting nor relevant as a politician. His lasting contribution to the Croatian culture and science is his gigantic and painstaking opus in historiography, including more than 450 works. Another relevant aspect of his work is the personal library he built during his life, containing more than 20,000 titles. When he died, those books became the most valuable part of the collection of the Croatian State Archives in Zagreb. As an expert archivist, Šišić diligently collected materials from numerous collections in Croatia, but also in Hungary, Austria, Britain, France, Italy, Belgium, Czech Republic and Slovakia.
Works
Hrvatski saborski spisi
Ljetopis popa Dukljanina
Korespodencija Rački-Strossmayer
Dokument o postanku Kraljevine SHS
Hrvatska povijest
Pregled povijesti hrvatskog naroda
Povijest Hrvata u vrijeme narodnih vladara, Zagreb, 1925
Poviest Hrvata za kraljeva iz doma Arpadovića , Zagreb, 1944