The national flag of Vatican City, also referred to as the flag of the Holy See, consists of vertical bicolour of yellow and white, with the white half charged with the emblem of the Holy See (a papal tiara and the crossed keys of Saint Peter). It was adopted in 1929, the year Pope Pius XI signed the Lateran Treaty with Italy, creating the new independent state of Vatican City.
It was modeled after the 1808 flag of the Papal States, a yellow-and-white bicolour defaced with the tiara and keys in the centre. It is one of only two national flags that use a 1:1 aspect ratio, along with the flag of Switzerland.