We've already reported that from 15 June, people in England will be required to wear face coverings on public transport.
There's a bit of controversy, because the British Medical Association (which represents doctors in the UK) says the rule should be extended so it's compulsory to wear masks in all public places where social distancing isn't possible.
That is the new guidance from the World Health Organization, which has changed its stance on fabric face masks.
But what are the rules right now in other countries?
In the US, legislation around masks is decided on a state-level - or even at a county-level in some cases. New York state, for example, requires people to wear masks in any public place where social distancing isn't possible. However, the Centers for Disease Control and Prevention (CDC) recommends everyone wear masks when out in public.
Things are a bit more straightforward in Germany, where mask-wearing has been mandatory on public transport and while shopping since 22 April.
France brought in a rule on May 10, making face masks compulsory while out in public, ahead of the start of their lockdown easing a day later.
And in Ireland, while people are advised to wear masks while out in public, it isn't actually mandatory.
Meanwhile, wearing masks in crowded places was far from uncommon in parts of Asia even before the coronavirus pandemic struck, especially if people were ill.
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