The Sejm of the Republic of Poland (; Polish: Sejm Rzeczypospolitej Polskiej) is the lower house of the Polish parliament. The Sejm is made up of 460 deputies, or Poseł in Polish (literally 'Envoy'). It is elected by universal ballot and is presided over by a speaker called the Marshal of the Sejm (Marszałek Sejmu).
In the Kingdom of Poland Sejm referred to the entire three-chamber parliament of Poland, comprising the lower house (Chamber of Envoys; Polish: Izba Poselska), the upper house (Senate; Polish: Senat) and the King. It was thus a three-estate parliament. Since the Second Polish Republic (1918–1939) Sejm has referred only to the lower house of the parliament; the upper house is called the Senat.