Around 45 million registered voters in England, Wales, Scotland and Northern Ireland will vote in elections across the UK on Thursday 5 May, dubbed "Super Thursday."
Britain is going to the polls in council, mayor and police commissioner elections - the biggest set of elections, outside of a general election for years and completely separate from the EU referendum on June 23.
Polling stations are open between 7am and 10pm. Any British citizen living in the UK who is 18 or over on 5 May can vote in England, Wales and Northern Ireland. The age limit is as low as 16 in Scotland.
You must need a polling card to vote - this should have been delivered in the post and it is too late to register for a new one.
Here's a guide to what's going on:
Council seats: Elections will take place at 124 councils, with 2,743 seats up for grabs using first-past-the-post system - that is the candidate with the most votes wins.
Parliamentary by-elections: MPs will be elected by first-past-the-post to represent Ogmore and Sheffield Brightside & Hillsborough.
This follows the resignation of Huw Irranca-Davies as Ogmore MP in March to fight for a Welsh Assembly seat, and the death in February of Sheffield Brightside & Hillsborough's sitting MP Harry Harpham.
Mayors: Mayoral elections will be held in Bristol, Liverpool, Salford and London (see below).
Police and Crime Commissioners: PCCs will be elected for each of 36 force areas elected using the Supplementary Vote system.
The PCC election due in Greater Manchester has been cancelled as the commissioner's powers are due to be transferred to a new directly-elected mayor next year. London similarly has no PCC as powers overseeing the Met fall to the mayor.
London Mayor and Assembly
Mayor: Londoners can vote for the capital's Mayor for a four-year term, elected using the Supplementary Vote system.
Greater London Assembly: Fourteen members will be elected by first-past-the-post to represent individual constituencies and another 11 from party lists.
Scottish Parliament Elections: An additional member system will be used to elect 129 Members of the Scottish Parliament (MSPs) for a five-year term.
Seventy-three constituencies will elect by first-past-the-post, while a further eight electoral regions will each select 7 MSPs using proportional representation known as the additional member system.
This is to ensure each party's representation is reflective of the votes they received.
Welsh Assembly Elections: There are 60 members in the Welsh Assembly and they will be chosen for a five-year term.
Each of Wales' 40 constituencies will elect a candidate using the first-past-the-post system, while another 20 are elected across five larger constituencies via the additional member system.
Police and Crime Commissioner: A PCC will be elected for each of the four force areas - Gwent, Dyfed-Powys, North Wales, South Wales - using the Supplementary Vote system.
Northern Ireland Assembly Election: The full complement of 108 Members of the Legislative Assembly will be elected for a five-year term.
There are six representing each of the 18 constituencies, elected using the Single Transferable Vote, which sees voters rank six competing candidates in order of preference.