A ban on smoking in enclosed public places has begun across Wales.
The smoking ban will affect all enclosed public buildings
Pubs, restaurants, offices and public transport are all covered by the ban, which came into force at 0600 BST.
Those found smoking can face on-the-spot fines of £50, while those in charge of premises could also be fined for allowing smoking.
A similar ban is already in force in Scotland. Northern Ireland will follow suit on 30 April, and England will follow on 1 July.
Health bodies and politicians hope for long-term benefits to people's health and a reduction in passive smoking effects for non-smokers.
But some pro-smoking groups called the outright ban "draconian" and wanted more options made available.
Extra enforcement officers are being taken on to support trading standards enforcement teams.
The ban will cover offices to lorry cabs, hospitals to football grounds and theatre stages, with very few exemptions.
Philip Lay, retail director at SA Brain, Wales's biggest independent brewer and pub operator, said: "The only certainty is that business is going to go backwards for a while."
The brewery has built smoking areas at some pubs and put up umbrellas and outdoor heaters at others.
Mr Lay added: "At one pub we went a little bit further and actually lifted the roof off part of the pub to create a courtyard.
"The difficulty is in explaining to people what constitutes an area they can or cannot smoke in."
One pub in Swansea which took the plunge early said landlords had little to fear.
Regulars at the Cross Inn in Morriston, Swansea, have been going without a smoke with their pint since the start of the year.
Owners Ellen and Brian Evans, who both smoke, decided to take the step when they took over the pub and had it refurbished.
SMOKING BAN FACT-FILE
It affects all public, enclosed spaces
Smokers defying the ban face a £50 on-the-spot fine
Premises not enforcing it face fines of up to £2,500
No smoking signs must be displayed
Council trading standards teams will enforce the ban
Hotels, adult residential homes and mental health units will be allowed exemptions in some rooms
Mrs Evans said: "There were mixed feelings amongst the customers - some have welcomed it but others felt their rights had been taking away.
"A pint and a fag have gone hand-in-hand for generations.
"But we've got people who smoke who come here and they respect it's no-smoking and go outside.
"No-one has disrespected it in three months - enforcing it has not been a problem.
"We now have a lovely mix of older people and a lot of younger people - some who bring their children."
Mr Evans added: "I think in the first few weeks [after the ban comes into force] it's going hurt.
"But people will always want to go out for a drink to somewhere where there is an atmosphere."
Ben Cottam, of the Federation of Small Businesses in Wales, said: "It's inevitable - the debate has moved a long way past whether or not there should be a ban.
"We have certainly asked our membership to keep an eye on the enforcement and on whether the enforcement is heavy-handed and we will certainly be raising that with the assembly government."
The British Medical Association's secretary in Wales, Richard Lewis, said: "This is the greatest public health initiative in Wales for over a century. The BMA has campaigned hard for years for it."
Nia Jeffreys of Asthma UK Cymru said: "Tobacco smoke excludes people with asthma from public places, and 40% of adults with asthma say they avoid smoky pubs and restaurants."
Welsh rugby star Gavin Henson, whose girlfriend Charlotte Church quit the habit last year, launched a campaign to urge parents to stop smoking altogether and make their homes smoke-free.
But tobacco lobby groups called the new measures "draconian" and say the public would rather support more options than an outright ban.
Simon Clark of Forest said the "vast majority" of smokers would not quit.
"A consequence of the ban is that more people will smoke in the street, increasing cigarette litter, and more people may smoke at home in front of their children," he said.
"The best place to smoke is in a well-ventilated bar or restaurant but politicians have chosen to ignore what is blatantly obvious."