A national flag is a flag that symbolises a country and that can usually be flown by citizens of that country.

Both public and private buildings such as schools and courthouses often fly the national flag. In some countries, the national flags are only flown from non-military buildings on certain flag days.

There are three distinct types of national flag for use on land, and three for use at sea, although many countries use identical designs for several of these types of flag.

National Flags on land

On land, there is a distinction between state flags, civil flags, and war flags. State flags are those used officially by government agencies, whereas civil flags may be flown by anyone irrespective of whether they are linked to government. War flags are used by military organizations such as the army. In practice, many countries have identical flags for these three purposes, and very few countries have separate war flags. In both the United States and United Kingdom, the national flag is used for all three purposes. In a number of countries, however - notably those in Latin America - there is a distinct difference between civil and state flags. In most case, the civil flag is a simplified version of the state flag, the difference often being the presence of a coat of arms on the state flag which is absent from the civil flag.