The Coat-of-Arms of the City of Dublin was first granted officially in 1607 to the municipal authority, Dublin City Council, by Daniel Molyneux, Ulster King-at-Arms and Principal Herald of All Ireland. This 17th century Coat-of-Arms incorporates a far more ancient device, the Three Castles of Dublin, which has been the symbol of the city since the Middle Ages, and which is shown on the 13th Century Dublin City Seal (below).

The City Seal shows the Three Castles as three watchtowers surrounding one of the gates in the medieval City Wall. Dublin is evidently under siege; from the central watchtower two sentries sound the alarm, while on each flanking watchtower stands an archer, poised with a cross-bow. The scene is symbolic of the readiness of the citizens to defend the city, and it was probably not intended to depict any actual event.

With the passage of time, the three watchtowers became three separate castles, each one bearing three battlemented towers, as shown in the Coat-of-Arms (right). The sentries and archers were replaced by flames leaping from the towers on the castles. It is often mistakenly supposed that the Castles are on fire, but in fact the flames symbolise zeal; here they represent the zeal of the citizens in the defence of Dublin. Looking in more detail at the Coat-of-Arms, we see that the Three Castles are borne on a Shield which is supported by two female figures. To the left of the Shield is a figure representing Law, holding a Sword erect in one hand, and in the other an olive branch. To the right of the Shield is a figure representing Justice, likewise holding an olive branch in one hand, and in the other, a pair of Scales. At their feet beneath the Shield are groups of flowers, symbolising hope and joy. The Coat-of-Arms is completed by the city's motto in Latin which reads: "Obedientia Civium Urbis Felicitas". This may be translated: "Happy the city where citizens obey."

The Dublin City Coat-of-Arms is still in use today and is displayed on all municipal buildings. It is on street furniture such as lamp-posts and benches and in mosaic form in the floor of the Rotunda, City Hall. A modified form of the Coat-of-Arms is often used. This consists merely of the Shield bearing the device of the Three Castles. This logo is to be seen on all public notices issued by Dublin City Council.