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.

[2] The Holy See, which governs Vatican City, has ecclesiastical jurisdiction over the worldwide Catholic Church.

[7] The flag is described in Article 23 of the 2023 Fundamental Law of Vatican City State, with a visual model appended as Attachment A.

[7] The flag is described in Article 19 of the 1929 Fundamental Law of Vatican City State, with a visual model appended as Attachment A.

[8] The flag is also described in Article 20 of the 2000 Fundamental Law of Vatican City State, with a visual model appended as Attachment A.

[9][10] The 2000 Fundamental Law of Vatican City State's Attachment A, shows a square flag.

In this version, the visible inner lining of the papal tiara is colored red instead of white, and a different shade of yellow or gold is used in some portions of the coat of arms.