Dublin 4, also rendered as D4 and D04, is a historic postal district of Dublin, Ireland including Baggot Street Upper, the southernmost fringes of the Dublin Docklands, and the suburbs of Ballsbridge, Donnybrook, Irishtown, Merrion, Ringsend (including South Lotts and parts of Grand Canal Dock) and Sandymount, on the Southside of Dublin. Most of the area was known as Pembroke until 1930 when it was absorbed by the City of Dublin.

The headquarters of the national broadcaster RTÉ, the RDS, Merrion Centre, University College Dublin, Aviva Stadium, Google and a number of foreign embassies to Ireland are all located in Dublin 4.

It is Ireland's most expensive postcode. At the height of the Celtic Tiger economic boom, Shrewsbury Road in D4 was the sixth most expensive street in the world, with one property on the street selling for €58 million. As of 2022, the average property price in the district was almost €1 million.

Dublin 4 or its abbreviation, D4, is sometimes used as a pejorative adjective to describe Dublin's upper-middle class based on the perceived characteristics of residents of this area. However, it sometimes also used to refer to the Irish upper middle class in general, regardless of whether or not they live in the D4 area. In this sense the term signifies a set of attitudes said to be in opposition to those held by "the plain people of Ireland" by Irish commentators such as Desmond Fennell.

While the area has, for most of its existence, been seen as well-to-do, the use of the term D4 as an adjective emerged in the 1990s. The fictional jock Ross O'Carroll-Kelly was meant as a caricature of this.

The term has been used to describe the aspirational upper middle-class from south Dublin and also used by Fianna Fáil members who like to portray themselves as being on the side of "the plain people of Ireland".

Maeve Binchy's book, Dublin 4, contains a series of short stories set in the area.

A change in accent occurred between those born roughly before 1970 and those born in the early 1970s or later.