The Southside[1] (Irish: Taobh Ó Dheas) is the part of Dublin city that lies south of the River Liffey.

(Malahide, one of the wealthiest areas in Ireland, is on the Northside, for example, whereas low-income districts like Jobstown and Sallynoggin are south of the Liffey.)

Beyond the city centre, the Southside (in the geographical sense) includes the districts named here, most of the names being old, though many were until recent times rural townlands: Traditionally, Dublin postal districts on Southside begin with even numbers, while those of the Northside begin with odd numbers.

College Green for example, is in the city's D02 district—simply called "Dublin 2" in everyday speech—whereas the outer suburb of Tallaght is in D24.

The outer edges of the Southside and substantial parts of Dun Laoghaire-Rathdown contain those new "A" postcode areas that have been assigned to southern Dublin (some "A" areas are situated in County Wicklow and County Meath and others lie across the Liffey in northern Fingal).