Norway has introduced a nationwide ban on smoking in restaurants and bars - following a similar move in Ireland.
About a quarter of Norwegians smoke
The Norwegian government says the ban is needed to protect people who work in the catering industry from the effects of second-hand smoke.
Opinion polls suggest a majority of Norwegians support the change, which permits smoking outdoors.
Ireland introduced its ban in March, and has hailed the move as a success.
Other countries including Tanzania, South Africa and the Netherlands, as well as parts of the US, have also introduced bans or restrictions.
Norwegian Health Minister Dagfinn Hoybraten said the change was not conceived to reduce smoking, but that it would be a positive secondary effect.
About 26% of Norwegian adults are smokers, high above the World Health Organisation's recommended maximum of 20%.
A BBC correspondent in Oslo says street-side restaurants have mushroomed to cater for smokers during Norway's long summer nights.
"We hope that business won't be hit," an Oslo nightclub manager told Reuters news agency.
"It'll take a few months to find out, but the biggest uncertainty is how the law will be applied. Will be lose our licence if someone has a cigarette and we can't persuade them to stop?" he added.
Bar and restaurant owners are responsible for upholding the ban, and face hefty fines for allowing smokers to keep puffing.