Humanities › Geography Union Jack The Union Jack Is a Combination of the Flags of England, Scotland, and Ireland Share Flipboard Email Print The Union Jack Flag. Geography Key Figures & Milestones Basics Physical Geography Political Geography Population Country Information Maps Urban Geography By Matt Rosenberg Geography Expert M.A., Geography, California State University - Northridge B.A., Geography, University of California - Davis Matt Rosenberg is an award-winning geographer and the author of "The Handy Geography Answer Book" and "The Geography Bee Complete Preparation Handbook." our editorial process Matt Rosenberg Updated April 02, 2017 The Union Jack, or Union Flag, is the flag of the United Kingdom. The Union Jack has been in existence since 1606, when England and Scotland merged, but changed to its current form in 1801 when Ireland joined the United Kingdom Why the Three Crosses? In 1606, when England and Scotland were both ruled by one monarch (James I), the first Union Jack flag was created by merging the English flag (the red cross of Saint George on a white background) with the Scottish flag (the diagonal white cross of Saint Andrew on a blue background). Then, in 1801, the addition of Ireland to the United Kingdom added the Irish flag (the red Saint Patrick's cross) to the Union Jack. The crosses on the flags relate to the patron saints of each entity - St. George is the patron saint of England, St. Andrew is the patron saint of Scotland, and St. Patrick is the patron saint of Ireland. Why Is It Called the Union Jack? While no one is quite certain where the term "Union Jack" originated, there are many theories. "Union" is thought to come from the union of the three flags into one. As for "Jack," one explanation states that for many centuries a "jack" referred to a small flag flown from a boat or ship and perhaps the Union Jack was used there first. Others believe that "Jack" could come from the name of James I or from a soldier's "jack-et." There are plenty of theories, but, in truth, the answer is that no one knows for sure where "Jack" came from. Also Called the Union Flag The Union Jack, which is most properly called the Union Flag, is the official flag of the United Kingdom and has been in its current form since 1801. The Union Jack on Other Flags The Union Jack is also incorporated into the flags of four independent countries of the British Commonwealth - Australia, Fiji, Tuvalu, and New Zealand.