New legislation has come into force in western parts of the Irish Republic to promote the use of the Irish language.
English place names no longer have legal status in the Gaeltacht, where Gaelic is traditionally spoken.
More than 2,000 towns, villages and crossroads in the Gaeltacht are commonly known by both their Irish and English names.
But from Monday, only the Gaelic versions may be used in government documents or ordnance survey maps.
For example, two villages on the Dingle peninsula in northwest Kerry, generally known by their English names, Dunquinn and Ventry, must now be identified on signs and government documents as Dun Chaoin and Ceann Tra.
The Gaeltacht encompasses the most westerly parts of counties Cork, Donegal, Galway, Kerry and Mayo and their nearby islands.
Other regions affected include several pockets in County Meath, northwest of Dublin, and County Waterford in the southwest, where Gaelic is widely spoken.
A second law introduces for the first time official Gaelic versions and spellings of hundreds of place names outside the Gaeltacht, where English has long been prevalent.
The English names will remain legal, but their Gaelic version must now be displayed alongside them.
Correspondents say the Irish constitution gives official status to both languages, but Dublin has spent several decades trying to keep Irish alive.