The book in Dublin will be open Friday, Saturday and Monday
A number of books of condolence are open after two terror attacks in Spain.
Fourteen people were killed and at least 100 others injured in Barcelona and Cambrils.
A white van drove through a crowd in the popular Las Ramblas area, while later six people were hurt in the coastal town of Cambrils after attackers ran them over in a car.
Those five attackers were shot dead by police.
Dublin's Lord Mayor Mícheál Mac Donncha opened a book of condolence on Friday at The Mansion House on Dawson Street.
The book will be open at the following times:
Mayor Mac Donncha said: "I was horrified to hear about the attacks on the people of Barcelona and Cambrils.
"Dublin and Barcelona have been sister cities since 1998 and have developed close ties throughout the years.
"I am opening this book of condolence to let the people of Dublin express their sympathies and solidarity to the families of those who died or were injured and to stand with the people of Barcelona."
A book of condolence has also been opened by Fingal County Council at County Hall, Swords and Civic Offices, Blanchardstown.
Clare County Council is also opening a book of condolence at Áras Contae an Chláir in Ennis.
And a book is also open at City Hall in Belfast.
Following yesterday's terror attack in #Barcelona a book of condolence will be opened at City Hall at 2.30pm.— Belfast City Council (@belfastcc) August 18, 2017
Anyone with concerns for the safety of Irish people in Spain can contact the Department of Foreign Affairs in Dublin on +353-1-4082000 or the Irish embassy in Madrid on +34-91-4364093