Local and European election polls and result details
21 May 2014 Last updated at 17:26 BST
Voters across the UK can take part in European elections between 07:00 and 22:00 BST on Thursday, but the results will not be announced until late on Sunday, or on Monday, after voting ends in other EU countries.
In addition, some parts of England have council and mayoral elections, and new members of the so-called super-councils in Northern Ireland will also be voted in, with those results announced late on Thursday, or on Friday.
Andrew Neil explains.
The BBC TV Vote 2014 programme with David Dimbleby starts at 22:35 BST on Thursday and runs overnight, plus Friday 12:00 to 13:00, and 14:00 to 18:00 on BBC Two, resuming at 21:00 Sunday on the News Channel, and also from 23:00 that night on BBC One. BBC Radio 4 and Five live will present joint programmes from midnight on Thursday, and 22:00 BST on Sunday with Jim Naughtie and Rachel Burden.