English: The flag of the municipality of Fredrikstad in the county of Viken, Norway. Its design is shared with the municipal arms, and shows a bear and a fortress. This motif goes back to Fredrikstad's first known seal from 1610, and is believed to be related to the seal and arms of the older and neighboring city of Sarpsborg, also showing a bear and a fortress. Sarpsborg was burned by Sweden during the Northern Seven Years' War, and this was the motivation for establishing a new city, Fredrikstad, in its stead.
As is often the case with old city seals, the contents of the 1610 seal eventually began being used in a shield shape as the city's arms. As the modern norms of Norwegian heraldry began taking shape during the 20th century, these arms were seen as complex and unheraldic. The arms were simplified and heraldized, which meant that the design would not only better conform to the high standards of Norwegian heraldry, but also be adaptable into a vexillologically appropriate banner of arms. The new flag and arms were approved by royal resolution 1967‐04‐21, the year marking the city's 400th anniversary.