The Swedish Empire refers to the Kingdom of Sweden between 1561 (after the Swedish conquest of Estonia) and 1721 (when Sweden officially ceded large areas in current south-eastern Finland to the emerging great power of Russia). During this time, Sweden was one of the great European powers. In Swedish, the period is called Stormaktstiden, literally meaning "the Great Power Era". the beginning is then often taken as 1611 (when Gustavus Adolphus ascended to the throne) and the end as 1718 (death of Charles XII and end of most fighting in Great Northern War). To the increase in political power, most notably by becoming one of the two guarantee powers for the Peace of Westphalia, was added an increase of territory that allowed near complete realization of the dominium maris baltici concept. The start and end dates of the period varies between historians.

After the death of Gustavus Adolphus in 1632, the empire was, over lengthy periods, controlled by part of the high nobility, most prominently the Oxenstierna family, acting as tutors for minor regents. The interests of the high nobility contrasted with the uniformity policy, i.e., the upholding of the traditional equality in status of the Swedish estates favoured by the kings and peasantry. In territories acquired during the periods of de facto noble rule, serfdom was not abolished, and there was also a trend to set up respective estates in Sweden proper. The Great Reduction of 1680 put an end to these efforts of the nobility and required them to return estates once gained from the crown to the king. Serfdom, however, remained in force in the dominions acquired in the Holy Roman Empire and in Swedish Estonia, where a consequent application of the uniformity policy was hindered by the treaties by which they were gained.