The 1809 Instrument of Government, adopted on 6 June 1809 by the Riksdag of the Estates and King Charles XIII, was the constitution of the Kingdom of Sweden from 1809 to the end of 1974. It came about as a result of the Coup of 1809, in which King Gustav IV Adolf was deposed. The promulgation of the constitution marks the point at which Sweden transitioned from the absolute monarchy of the Gustavian era into a stable, constitutional monarchy adhering to the rule of law and significant civil liberties.

Riksdag of the Estates was the name used for the Estates of Sweden when they were assembled. Until its dissolution in 1866, the institution was the highest authority in Sweden next to the King. It was a Diet made up of the Four Estates, which historically were the lines of division in Swedish society:Nobility Clergy Burghers Peasants