The House of Vasa (Swedish: Vasaätten, Polish: Wazowie, Lithuanian: Vazos) was an early modern royal house founded in 1523 in Sweden, ruling Sweden 1523–1654, the Polish–Lithuanian Commonwealth 1587–1668, and the Tsardom of Russia 1610–1613 (titular until 1634). Its agnatic line became extinct with the death of King John II Casimir of Poland in 1672.
The House of Vasa descended from a Swedish 14th-century noble family, tracing agnatic kinship to Nils Kettilsson (Vasa) (died 1378), fogde of Tre Kronor Castle in Stockholm. Several members held high offices during the 15th century. In 1523, after the abolition of the Kalmar Union, Gustav Eriksson (Vasa) became King Gustav I of Sweden and the royal house was founded. His reign is sometimes referred to as the beginning of the modern state of Sweden, which included the King's break with the Roman Catholic Church during the Protestant Reformation and the foundation of the Church of Sweden.
However, his eldest son and successor Erik XIV of Sweden was overthrown by Gustav's younger son, King John III of Sweden. John III married a Catholic Polish princess, Catherine Jagiellon, leading to the House of Vasa becoming rulers of Poland.
Their Catholic son Sigismund III Vasa, then ruler of a short-lived Polish–Swedish union, was usurped in 1599 by John's Protestant brother King Charles IX of Sweden in the War against Sigismund. The dynasty was split into a Protestant Swedish branch and a Catholic Polish one, which contended for crowns in subsequent wars.
The involvement of the famous Protestant general and King Gustavus Adolphus of Sweden in the Thirty Years' War gave rise to the saying that he was the incarnation of "the Lion of the North" (German: "Der Löwe von Mitternacht"). Yet, notably, his daughter and heiress Queen Christina of Sweden (1632–1654) abdicated in 1654 after converting to Catholicism, and emigrated to Rome. In Poland, John II Casimir of Poland abdicated in 1668. With his death, the royal House of Vasa became extinct in 1672, though the current King of Sweden, Carl XVI Gustaf, is descended from Gustav I through his paternal great-grandmother, Victoria of Baden, a descendant of Gustav I's great-great-grandson Adolphus Frederick II, Duke of Mecklenburg-Strelitz.