Which European country's flag is blue with a yellow cross? Sweden. The Swedish flag is a light-blue field carrying a gold or yellow Nordic cross, with the vertical bar shifted toward the hoist.
The cross design places Sweden within the Nordic flag tradition associated with Denmark, Norway, Finland and Iceland. Its Christian symbolism is common to Nordic crosses, while Sweden's blue-and-yellow colours are tied to its historic royal arms. Blue and gold appeared in Swedish heraldry by the medieval period, including the arms associated with King Magnus III in the late 13th century.
The precise origin of the flag is uncertain, and a popular legend says King Eric IX saw a golden cross in the sky during a 12th-century campaign in Finland. The earliest surviving images of a blue flag with a yellow cross date from the early 16th century. A royal warrant formally described the design in 1562, and Sweden's current flag was legally adopted on 22 June 1906.
A common mix-up is with Finland, whose Nordic cross is blue on white; Sweden reverses that dominant colour arrangement.