Unicode contains 26 regional indicator symbols.
The set covers the letters A through Z, with each regional indicator symbol corresponding to one alphabetic character. They are designed primarily to work in pairs, allowing software to interpret sequences such as the regional indicators for U and S as the United States flag emoji.
The number 26 refers to the individual symbols, not the number of possible flags. Combining any two symbols mathematically produces 26 × 26, or 676, ordered pairs. Unicode and related region data recognize only a subset of those pairs as valid flag sequences, so 676 is not the count of regional indicator symbols or currently supported national flags.
Regional indicator symbols occupy the Enclosed Alphanumeric Supplement block of Unicode. They were added to support a scalable flag-encoding approach instead of assigning a permanent standalone character to every national flag. This also explains why flag availability can vary between platforms: a sequence may be encoded correctly but rendered as letters, an empty box, or a flag depending on software support.