The widespread wearing of face coverings for travellers is to become compulsory in Scotland.
From Monday, they will be mandatory on all public transport, including taxis and private hire cabs.
The rules also apply to buses, trains, the Glasgow Subway, Edinburgh trams, aircraft and enclosed areas onboard ferries.
First Minister Nicola Sturgeon said face coverings "can help to reduce the risk of transmission".
Ms Sturgeon told MSPs: "If you have Covid, but maybe don't realise it because you don't have symptoms, a face covering reduces the risk of you passing the virus on to other people.
"And other people wearing face coverings help to protect you in a similar way."
She stressed the measure should not be seen as an "absolute safeguard"
It was still necessary to ensure physical distancing, hand washing and "good hygiene" to prevent infection.
The new rules on face coverings are being implemented as public transport becomes busier, with more people allowed to return to work.
Some exemptions will apply.
Children under five, people with breathing difficulties, and those with a physical condition which makes it hard to keep a mask in place will not be required to wear a face covering.
Drivers who are already behind a protective shield will be exempt.
The Scottish government will consult on whether a similar rule should be introduced in shops.
Non-essential shops are expected to be able to open from 29 June, and a decision on face coverings will be made before then.