Oscar II (Oscar Fredrik; 21 January 1829 – 8 December 1907) was King of Sweden from 1872 until his death in 1907, and King of Norway from 1872 to 1905.

Oscar II was King during a time when both Sweden and Norway were undergoing a period of industrialization and rapid technological progress. His reign also saw the gradual decline of the Union of Sweden and Norway, which culminated in its dissolution in 1905. He was subsequently succeeded as King of Norway by his grandnephew Prince Carl of Denmark under the regnal name Haakon VII, and as King of Sweden by his eldest son, Gustaf V.

Oscar II is the paternal great-great-grandfather of Carl XVI Gustaf, King of Sweden since 1973. Margrethe II, Queen of Denmark is his descendant through his son Gustaf V. Harald V, King of Norway since 1991, Philippe, King of the Belgians since 2013, and Henri, Grand Duke of Luxembourg since 2000, are also descendants of Oscar II, all through his third son Prince Carl, Duke of Västergötland.