The Swedish Empire or the Great Power era (Swedish: stormaktstiden) was the period in Swedish history spanning much of the 17th and early 18th centuries during which Sweden was a European great power that exercised territorial control over much of the Baltic region. During this period it also held territories on the North Sea and some overseas colonies, including New Sweden. The beginning of the period is usually taken as the reign of Gustavus Adolphus, who ascended the throne in 1611, and its end as the loss of territories in 1721 following the Great Northern War.

After the death of Gustavus Adolphus in 1632, the empire was controlled for lengthy periods by part of the high nobility, such as the Oxenstierna family, acting as regents for under-aged monarchs.

After its victories in the Thirty Years' War and the subsequent Peace of Westphalia Sweden was granted territories in northern Germany. Sweden reached the height of its power during the Northern War of 1655–1660, when its primary adversary, Denmark–Norway, was neutralized by the Treaty of Roskilde in 1658. Denmark–Norway was forced to give up a third of its territory to save the rest. Although the reign of Charles XII would see initial Swedish victories in the Peace of Travendal (1700) and the Treaty of Altranstädt (1706), he would go on to lead a campaign in Russia that would end in a decisive defeat at the Battle of Poltava. The Russian victory put an end to Sweden's territorial expansion, and by the time of Charles XII's death in 1718 the Empire had been severely diminished both territorially and militarily. Finland was ceded to Russia in 1809, and Sweden's last remaining continental territory (Swedish Pomerania) was ceded to Denmark in exchange for Norway following the Napoleonic Wars.

Sweden emerged as a great European power under Axel Oxenstierna and King Gustavus Adolphus. As a result of acquiring territories seized from Russia and the Polish–Lithuanian Commonwealth, as well as its involvement in the Thirty Years' War, Sweden found itself transformed into the leader of Protestantism.

During the Thirty Years' War, Sweden managed to conquer approximately half of the member states of the Holy Roman Empire. The fortunes of war would shift back and forth several times. After its defeat in the Battle of Nördlingen (1634), confidence in Sweden among the Swedish-controlled German states was damaged, and several of the provinces refused further Swedish military support, leaving Sweden with only a couple of northern German provinces. After France intervened on the same side as Sweden, fortunes shifted again. As the war continued, the civilian and military death toll grew, and when it was over, it had led to severe depopulation in the German states. Although exact population estimates do not exist, historians estimate that the population of the Holy Roman Empire fell by one-third as a result of the war.

Sweden founded overseas colonies, principally in the New World. New Sweden was founded in the valley of the Delaware River in 1638, and Sweden later laid claim to a number of Caribbean islands. A string of Swedish forts and trading posts was constructed along the coast of West Africa as well, but these were not designed for Swedish settlers.

At the conclusion of the Thirty Years' War, the Peace of Westphalia (1648) granted Sweden territories as war reparations. Sweden demanded Silesia, Pomerania (which had been in its possession since the Treaty of Stettin (1630)), and a war indemnity of 20,000,000 Riksdaler.

Through the efforts of Johan Oxenstierna and Johan Adler Salvius it obtained: