The article characterises research into the history of parliamentarism of the Polish-Lithuanian Commonwealth conducted in Polish historiography in the 19th century and in the interwar period (until 1939). Due to the wide problematic and chronological range the publication is of a review nature. It presents profiles of the main researchers and the most important histori-ographical views on the history of the Sejm in the 16th-18th centuries, represented among others by Adolf Pawinski, Walerian Kalinka, Michal Bobrzynski, Wladyslaw Smolenski, Oswald Balzer, Stanislaw Kutrzeba, Stanislaw Starzynski, and Wladyslaw Konopczynski. This research was of a multi-faceted nature, and was undertaken both by historians of social and political history, as well as historians of law, with particular emphasis on the legal and constitutional research conducted at that time.