The Dublin postal districts are used by the Irish Post Office, An Post to make sorting and pre-delivery handling of mail more efficient. The odd-numbered codes specify addresses north of the River Liffey, and the even-numbered ones refer to the Southside.

The city centre business districts mostly lie within Dublin 1 and Dublin 2. While the codes are mostly numerical only, Dublin 6W is an exception, defined when An Post attempted to create a new postal area in south Dublin. Residents of some areas, citing property devaluation, objected to the proposed amalgamation of their areas with those they considered to be less valuable.

Of all the post codes, Dublin 4 (D4) is by far the most famous, arousing various emotions in Dubliners and Irish country people alike. While the lingua franca of D4 is nominally English, many words suffer a distorted pronunciation. Wits in D4-speak render the proper title of Bord Gais - as "Bored Gosh", for example. Other examples include "Unpussed" for the national post office - An Post, alright' as 'awlrite', 'car' as 'core' and 'phone' as 'phewn'. The area is famed for its upper class almost snobbish ways. This is due to the large number of fee paying private secondary schools in the area which are famed for the popularity in rugby - considered a mainly upper and middle class sport. However these attitudes reflect a charicatured attitude, perhaps unfairly, towards "Southsiders" in general.

Many foreign embassies are located in D4, due to the prevelance of large Georgian, Edwardian and Victorian buildings.

The book The Orange Mocha-Chip Frappuccino Years features the character Ross O'Carroll Kelly (note the double barrelled surname, which is considered pretentious) who embodies the D4 stereotype. The entire book is written phoenetically in the stereotypical D4 style.