Anational flag is a one that represents and symbolizes acountry ornation-state.Flags — and the related(royal) standards,ensigns,banners, andpennons / pennants — come in manyshapes and designs, which often indicate something about what the flag represents, but generally national flags are rectangular or sometimes square-shaped.

Commondesign elements of flags include shapes ascharges — such ascrescent moons,crosses,stars,stripes, andsuns — layout elements such as including acanton (a rectangle with a distinct design, such as another national flag), and the overall shape of a flag, such as theaspect ratio of a rectangular flag — whether the flag is square or rectangle, and how wide it is — or the choice of a non-rectangular flag. Sometimes these flags are used as a short-hand guide torepresent languages on tourist information or versions of websites on the internet.

Many countries with sharedhistory,culture,ethnicity, orreligion havesimilarities in their flags that represent this connection. Sets of flags in this list within the same category may represent countries' shared connections — as with the Scandinavian countries exhibiting theNordic cross on their flags — or the design similarity may be acoincidence — as with the red and white flags ofIndonesia andMonaco andPoland.

For clarity, unless stated, allflags shown are thecivil flag ( − thevexillological symbol of identification fromFIAV, Fédération internationale des associations vexillologiques) or thenational flag () of thenation state / sovereign country recognised as such by theUnited Nations — thestate flags, ( − usually those of the government), along with the flags ofautonomous countries, regions, and territories of a UN nation state are annotated in italics as such.

Historical flags are marked with the vexillological symbol and flags that are used widely, but without any legal basis (de facto), are marked with the vexillological symbol.

Most flags are rectangular / oblong. InNordic nations, some haveswallowtail shapes as the state flag, though the civil flag is oblong. The only nation state to fly a civil flag that is non-rectangular is   Nepal.

A great many national flags have a single defined aspect ratio. The most commonaspect ratio is 2:3, followed by 1:2, with only a few being 1:1 (square-shaped). Some nations' flags have multiple acceptable ratios, or do not define any ratio at all, such as theUnion Jack of the United Kingdom having its commonest aspect ratios of 1:2 followed by 2:3.

The following are the government / state flag only — thecivil flag is without the coat of arms.

Historical flags ()

• 
  Flag of the East India Company
  (1600→1707 — The company refused to use theKing's Colours of 1606 until theAct of Union (1707))
• 
  Flag of the British East India Company
  (1707→1801)
• 
  Flag of the British East India Company
  (1801→1858)
• 
  Flag of Canada
  (1868→1921)
• 
  Flag of Canada
  (1921→1957)
• 
  Flag of Canada
  (1957→1965)
• 
  Flag of the Kingdom of Hawaiʻi
  — a 1:2 canton and 9 stripes
  (1795→1893 —The Sandwich Islands)
• 
  Flag of the Republic of Hawaiʻi
  — a 1:2 canton and 8 stripes
  (1893→1959 —unincorporated unorganized territory of the US)
• 
  Flag of South Africa
  (1928→1994)
• 
  TheContinental Union Flag / The FirstFlag of the United States
  (1776→1777)

Notably, the British Union Jack features in many territorial and sub-national flags usually based on theRed Ensign, ( — e.g. Bermuda), orBlue Ensign, ( — e.g. New South Wales). TheWhite Ensign () is used in a few cases with backgrounds of other colours, (e.g. The British Antarctic Territory and Niue), or a unique pattern in the field, (e.g. The British Indian Ocean Territory and Hawaii). Notably, theRoyal Air Force Ensign is used as the basis for Fiji and Tuvalu flags. Some flags use the Union Jack other than at the canton, (e.g. British Columbia). Unofficial flags () also use it, (e.g. The Ross Dependency of Antarctica).