Wales has introduced a complete ban on smoking in enclosed public places.
The ban means smoking is no longer permitted inside the country's bars, pubs restaurants and hotels (except for designated smoking guestrooms).
Operators must have their bilingual "no smoking" signs placed prominently about their premises or face a hefty fine (a minimum of £200 and up to £1,000 if it goes to court).
Wales's Fist Minister Rhodri Morgan said: "This is the single most important public health measure that the Assembly has introduced."
He added that the legislation would make an enormous difference to people regularly exposed to tobacco smoke in work, such as pub staff.
Second-hand smoke is estimated to cause 400 premature deaths a year, according to the Assembly.
Any premises failing to stop smoking taking place can be fined up to £2,500. Individuals face a spot-fine of £50 for smoking, which will rise to £200 if it goes to court.
By Chris Druce
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