The Union Flag or Union Jack is the name of the flag of the United Kingdom.
Union flag may also refer to:
- Flag of the African Union
- Flag of Europe, also called the Flag of the European Union
- Flag of the Kalmar Union
- Flag of the Soviet Union
- Flag of the Union of South Africa
- Grand Union Flag, the first national flag of the United States
- Flag of the United States (also called "Union")
- Union flag, of the Union during the American Civil War
- Union mark of Norway and Sweden
- The Union Flag, newspaper published in Tennessee