The Diet of Porvoo (Finnish: Porvoon maapäivät, or unhistorically Porvoon valtiopäivät; Swedish: Borgå lantdag; Russian: Боргоский сейм), was the summoned legislative assembly to establish the Grand Duchy of Finland in 1809 and the heir of the powers of the Swedish Riksdag of the Estates. The session of the Diet lasted from March to July 1809.
During the Finnish War between Sweden and Russia, the four Estates of Russian-occupied Finland (nobility, clergy, burghers and peasants) were assembled in Porvoo (Borgå) by Tsar Alexander I, the new Grand Duke of Finland, between 25 March and 19 July 1809.
