By Ania Lichtarowicz
BBC News health reporter
The world's first global health treaty - the Framework Convention on Tobacco Control - has come into force.
About five million people die each year from smoking-related diseases
The anti-smoking pact has been signed by 168 countries, and ratified by 57 of them, which will now have to tighten their anti-tobacco laws.
The treaty demands health warnings on cigarette packets and bans on tobacco advertising within five years.
Every year five million people die from smoking-related diseases - a number set to double by 2020 if nothing is done.
So the World Health Organization has designed the FCTC to force countries to implement stricter tobacco legislation.
Dr Douglas Bettcher, the co-ordinator of the FCTC Unit, explained why the world needed binding international law on tobacco:
Key requirements of treaty
Ban tobacco advertising, sponsorship and promotion, where constitutions allow, within five years
Tobacco packaging must include health warnings covering at least 30% of packet within 3 years
Introduce measures to protect people from second-hand tobacco smoke in public places
Draw up strategies to combat smuggling
Adopt tax policies which discourage smoking
"The world community was faced and appalled by the mushrooming number of needless deaths due to tobacco-related diseases."
The 57 countries that have agreed to be bound to the FCTC will only be able to sell cigarettes with health warnings on packets.
Within five years they will have to ban tobacco advertising, promotion and sponsorship, as well as reducing exposure to second-hand smoke - basically banning smoking in public places.
The industry had initially opposed the treaty but Dr Chris Procter of British American Tobacco says that on the whole it is a good thing:
"There's a fair will in the international community to make the Framework Convention work.
"As a member of British American Tobacco, we're looking forward to working with the World Health Organization and with the Framework Convention to see how to make this work the best."
How effective the treaty will be remains to be seen.
Although countries including the UK, India, Canada and Australia have all signed and ratified, some major players such as the US have not yet fully committed to it.