The Catholic Papal flag consists of two vertical bands, one of gold or yellow (hoist side) and one of white with the crossed keys of Saint Peter and the Papal Tiara centered in the white band. The crossed keys consist of a golden and a silver key, in which the silver key is placed in the dexter position. Despite the widespread idea that the flag is square, its proportions are not specified in the constitution, and in response to the German nunciature, it was explicitly mentioned that the flag is not square.
The coat of arms of Vatican City is present in the white half. The coat of arms consists of:
- the papal tiara (as used under the pontificate of Pius XI);
- the two keys which represent the Keys of Heaven (according to the Gospel of Matthew 16:19) given by Jesus Christ to St Peter. The popes are regarded as the successor of Peter, and the gold and silver keys have been significant elements in the symbolism of the Holy See since the 13th century. The gold represents spiritual power, while the silver key represents worldly power. The order of the keys on the coat of arms of Vatican City is the reverse of the coat of arms of the Holy See, in order to distinguish between the two entities.
- a red cord connecting the keys.
The yellow and white of the flag also refer to the keys – in heraldic terminology, there is no distinction between yellow and gold (the metallic color or), nor between white and silver (argent).
The placing of gold and white side-by-side is considered a violation of the rule of tincture; it can be difficult for the eye to distinguish between the two bands.