Millions of people across Britain will cast a ballot on Thursday in the biggest set of votes since the 2019 general election.
Elections for the Scottish Parliament, the Welsh Senedd, and 143 councils and 13 mayors in England are happening.
A Westminster by-election is also taking place in Hartlepool.
Up to 48 million people are eligible to vote across Britain. Polling stations open from 07:00 to 22:00 BST, with the results expected over several days.
Many of the elections – on what has been dubbed “Super Thursday” – were due to be held last year but the pandemic forced their delay, meaning that more than usual are taking place this time.
Voters in England and Wales will choose 39 chief and crime commissioners, while the make-up of the London Assembly is to be decided.
The weather is set to be chilly across Britain on Thursday, with scattered showers and sunny intervals forecast over England and Wales. In Scotland, heavier rain is predicted, with some snow over hills in northern areas.
So warm and waterproof clothing is recommended, as voters are expected to endure longer queues than normal at polling stations, which are observing strict Covid protocols, including the frequent cleaning of booths.
Social distancing will be in place and the public are encouraged to bring their own pencils for completing ballots.
The Democracy Club group – which encourages voting – says more than 35,000 venues across Britain will serve as polling stations.
These include more than 50 restaurants and cafes, 30 museums, 120 cricket clubs and pavilions and 13 boxing clubs.
When will the results be known?
Some counting will take place overnight on Thursday, including for the Hartlepool by-election, where a result is expected in the early hours of Friday.
Results for all 60 seats in the Welsh Senedd will be known on Friday.
Scotland starts counting in some areas on that day, but there will not be a final result until Saturday, or possibly Sunday.
Counting in council areas in England will take place on Friday, and continue over the weekend in some areas.
And 12 of the counts for 39 police and crime commissioners elected in England will not begin until Monday.