Millions of people in London are heading to the polls to vote for their new Mayor and assembly member.

Today, Boris Johnson MP ends his eight year reign at the helm of City Hall, to be replaced, most likely, by Conservative colleague Zac Goldsmith or Labour rival Sadiq Khan.

They face stiff competition from candidates including the Liberal Democrat Caroline Pidgeon, the Green candidate Sian Berry and UKIP's Peter Whittle. 

Not only will London have a new Mayor, who looks after big issues like transport, planning and the environment, but the Greater London Authority, which has 25 members, will look different too.

The assembly members are made up of constituency candidates, each member covering two boroughs, and list candidates, who 'top-up' the make-up of the assembly, to create a proportional system. 

How do they compare? We sat down with the Mayoral candidates one by one in the run up to today, and our interviews are here: 

Conservative Party: Tory mayoral hopeful Zac Goldsmith talks Jeremy Corbyn, tax credit cuts and Heathrow expansion

Labour Party: "I'll probably die in Tooting": Our interview with Labour's mayoral candidate Sadiq Khan on Crossrail, police cuts and Nandos

Green Party: Berry on renters' unions, air pollution and more: Green Party candidate Sian Berry discusses her mayoral campaign

Women's Equality Party: "Aiming to get the job done": Women's Equality Party mayoral candidate Sophie Walker talks transport, housing and crime priorities in bid for city hall

UKIP: London's only gay mayoral candidate talks arts, housing, tube strikes and why London is better out of the EU

Respect Party: George Galloway on combating extremism, banning trucks in London and his rival's "miserable" campaign

The other candidates are:

David Furness - British National Party

Paul Golding - Britain First

Lee Eli Harris - Cannabis is Safer than Alcohol

Ankit Love - One Love Party

Prince Zylinski - Independent

How about the GLA candidates?

If you live in south east London, check out who is running for a seat in your borough, here.

If you live in any other part of London, you can see the candidates on the London elects website, here

So how do you vote?

The Mayoral and London Assembly elections are run slightly differently to those across the rest of the country. In the Mayoral elections, voters have two preferences - first and second.

As it sounds, cast one vote in the first preference column for the candidate you most want to win.

In the second column, cast one vote for your second favourite. 

The votes will be counted first by first preference and then by eliminating candidates at the bottom of the list and redistributing those votes by the second preference.

So for example, if someone votes for Sian Berry and she fails to secure a large majority, that person's second vote would be given to help them in their tally. 

The vote will still be counted if only one is cast, so cast one or both. 

For the London Assembly, two ballot papers will be given to the voter.

The first one is for the constituency representative, the person who will be directly linked to represent the borough you live in.

Cast one vote for the person you want to win.

The second ballot paper is for the London-wide seat. The London Assembly is topped up with members from parties in order to reflect the overall vote in a proportional manner.

Cast one vote for the party you want to be represented in City Hall. 

Where can I vote? What if I lost my polling card?

Polling stations open at 7am and close at 10pm. If you arrive at the polling station before 10pm, you will be allowed to vote, even if there is a long queue. 

There will be two people there, who will ask your name and address and take you off their list. 

Your polling card simply confirms you are registered to vote and where to do so. It is not needed on the day.

Polling stations are listed on local authority websites. You may need to check with your authority, as you cannot vote at any station and must vote at the one you have been assigned to. 

If you received a postal vote, but forgot to send it, drop it in to any polling station in your area before 10pm. 

If you live in Bexley, click here.

If you live in Bromley, click here.

If you live in Greenwich, click here

If you live in Lewisham, click here

If you live in Kingston, click here

If you live in Richmond, click here.

If you live in Wandsworth, click here.

If you live in Merton, click here.

If you live in Sutton, click here

If you live in Croydon, click here

No luck? Click here.

When will I know who has won?

The counting of the votes will not start until 8am on Friday, May 6.

At City Hall, the votes for the Mayor will be counted. The time of the results will depend on turnout - the more voters cast their ballots, the later the result will be. 

The count for the south east London boroughs will be held in the ExCel centre. 

The count for the south west London boroughs will be held at Olympia.

You can follow all of the coverage throughout the day on our live blog.