The coats of arms of the Holy See and Vatican City State in the form that combines two crossed keys and a tiara used as a coat of arms of the Holy See have origins attested from the 14th century. The combination of one gold and one silver key is somewhat later.

The coat of arms of Vatican City State, a sovereign entity established by the Lateran Treaty of 11 February 1929, was adopted by the Fundamental Law of the new state on 7 June 1929, and has its coat of arms defined by law as having the silver key in bend and the gold key in bend sinister.

For decades after the creation of the Vatican State, the arrangement of the keys in the Holy See's coat of arms as described in these sources distinguishes it from that of Vatican City State by a reversing of the gold and silver keys. However, such form of the coat of arms has not been used by the Holy See for decades: in all official events and in the diplomatic missions of the Holy See abroad, it is always the regular Vatican City flag (with the gold key pointing upwards to the right and the silver key pointing upwards to the left) that is flown, and the Vatican now only uses the Holy See's coat of arms in monochrome, which renders it in practice one and the same as the coat of arms of Vatican City.