Star Wars (Multimedia Franchise)

The Galactic Republic is the government spanning most of the galaxy in the Star Wars prequels. The roots of the Republic go back around 25,000 years, but the present Republic was reorganized after the Ruusan Reformation about 1000 years prior to the events of the films.

The flag of the Galactic Republic is the seal of the Republic on a field of crimson, the color used on official vessels (military and governmental) of the Republic, as seen in Star Wars Episodes I, II, and III.

Note that this flag does not appear in the films but is taken from a drawing published by an official Lucasfilm site (Holonet News). A copy of this drawing can be found here
J.T. Tate, 4 July 2005

Interestingly, this is the symbol of the Empire in the original three movies, while the rebellion uses a different one, somewhat similar to a stylized bird.
Nathan Lamm, 5 July 2005

That is to be expected, as the Empire legally emerged from the Old Republic, building on its legitimacy and changing it "from within" under a non-revolutionary propaganda — and keeping its symbols.
António Martins-Tuválkin, 5 July 2005

The seal being a black and white round emblem, makes this one more mock Nazi fictional flag . This may have happened as the Empire is presented in the original movies as something evil (and "nazi"="evil" in Hollywoodese) and only later its transformation from the "unevil" Old Republic is shown as a relatively recent change, with no place for a radical symbol change — also because, as mentioned, the transition was made from within and under a blanket of legitimacy.
António Martins-Tuválkin, 10 July 2005

Galactic Empire

The symbol use by the Galactic Empire is similar to the Galactic Republic one but not the same. In fact, as shown by the diagram above, the Republic had an eight-pointed symbol, and the Confederacy had six points, as does the Empire, so the Imperial Seal is probably the Republic and Confederacy combined. (The seal I found of the Empire has black and white reversed, but sometimes you see it the other way. I have yet to see the Republic's colors reversed.)
J.T. Tate, 4 July 2005

Confederacy of Independent Systems

The Confederacy of Independent Systems (also known as the Separatists) was led by Count Dooku of Serenno, a former Jedi Knight. The members of the CIS considered the Republic too corrupt to be saved and seceded to form their own government. The CIS was a looser affiliation than the Republic, and many of its member governments were from corporate, monetary, and trade interests.

The secession of the Confederacy ignited what was called the "Clone Wars", wherein Republic clone forces under the Jedi Knights fought the separatists. Eventually, the Republic was able to defeat the Separatists with the death of Count Dooku and military leader General Grievous at the hands of the Jedi. The CIS seal, as seen in Star Wars Episode III, is a hexagonal shape divided into wedges, with a smaller, darkened hexagon in the center. flag is this seal upon a (vertical) field of blue, which is the color used on official Confederacy military and government ships, also seen in Star Wars III.
J.T. Tate, 4 July 2005

The Rebellion & New Republic

The rebellion uses a symbol somewhat similar to a stylized bird.

I wonder what the Rebellion (and later New Republic) symbol is supposed to be. I think I once saw it described as a symbol of Alderaan, but I'm not sure.
Nathan Lamm, 5 July 2005