History was made last night as time was called on smoke-filled pubs, restaurants and other public places right across Northern Ireland.
The long-awaited ban took effect at 6am this morning, with health campaigners predicting that it could save 250 lives a year.
The measure has overwhelming public support, despite fears that it could hit pub trade.
It brings Northern Ireland into line with the Republic and Scotland and is being introduced two months ahead of similar legislation in England.
A number of bars last night held special evenings to mark the final hours of smoking indoors.
Customers expressed mixed views on the ban as the clock ticked down.
Health Promotion chief Dr Brian Gaffney said today was a time for celebration.
"Everyone has the right to clean air and from today, as people across Northern Ireland make their way into work, they will know that they are guaranteed protection from the deadly effects of second-hand smoke."