The Treaty of Nystad (Russian: Ништадтский мир, Finnish: Uudenkaupungin rauha, Swedish: Freden i Nystad) was the last peace treaty of the Great Northern War. It was concluded between the Tsardom of Russia and Swedish Empire on 30 August (O.S.) / 10 September (N.S.) 1721 in the then Swedish town of Nystad (Finnish: Uusikaupunki), after Sweden had settled with the other parties in Stockholm and Frederiksborg.

During the war, Peter I of Russia had occupied all Swedish possessions on the eastern Baltic coast: Swedish Ingria, where the new Russian capital St. Petersburg was constructed since 1703; Swedish Estonia and Swedish Livonia, which had capitulated in 1710, and Finland. In Nystad, Frederick I of Sweden formally recognized the transfer of Estonia, Livonia, Ingria, and Southeast Finland (Kexholmslän and part of Karelia) to Russia in turn for two million silver thaler, while the bulk of Finland was returned to Sweden.

The treaty enshrined the rights of the Baltic-German nobility within Estonia and Livonia to maintain their financial system, right to self-government and Lutheran religion, the German language and the existing customs border; this special position in the Russian Empire was reconfirmed by all Russian Tsars from Peter the Great to Alexander II.

Charles XII also Carl of Sweden, Swedish: Karl XII, Latinized to Carolus Rex, Turkish: Demirbaş Şarl (which means Charles the Habitué or Charles the Fixture) (17 June 1682 – 30 November 1718) was the King of the Swedish Empire from 1697 to 1718. Charles was the only surviving son of King Charles XI of Sweden and Ulrika Eleonora the Elder, he assumed power after a seven-month caretaker government at the age of fifteen.

In 1700, a triple alliance of Denmark–Norway, Saxony–Poland–Lithuania and Russia launched a threefold attack on the Swedish protectorate of Swedish Holstein-Gottorp and provinces of Livonia and Ingria, aiming to draw advantage as Sweden was unaligned and ruled by a young and inexperienced king, thus initiating the Great Northern War. Leading the formidable Swedish army against the alliance, Charles had by 1706 forced to submission all parties but Russia.

Charles' subsequent march on Moscow ended with the dismemberment of the Swedish army at Poltava and Perevolochna, and he spent the following years in exile in the Ottoman Empire before returning to lead an assault on Norway, trying to evict the Danish king from the war once more in order to aim all his forces at the Russians. Two failed campaigns concluded with his death at the Siege of Fredriksten in 1718. At the time, most of the Swedish Empire was under foreign military occupation, though Sweden itself was still free. This situation was later formalized, albeit moderated in the subsequent Treaty of Nystad. The close would see not only the end of the Swedish Empire but also of its effectively organized absolute monarchy and war machine, commencing a parliamentarian government unique for continental Europe, which would last for half a century until royal autocracy was restored by Gustav III.