Image source, Getty Images

In tonight's debate, Harris and Trump’s mics will be muted unless it’s their turn to speak.

It’s the same rule as when Trump and Biden debated earlier this year - but the rule was only confirmed last week by ABC after days of bickering by the campaigns.

The Trump campaign wanted the ABC debate to be governed by the same rules agreed when Biden was the Democratic candidate.

With Biden out, the Harris campaign argued for having a “hot” mic - meaning it’s never turned off.

The Harris team said last month that “Trump should stop hiding behind the mute button”.

Trump told reporters last month that he'd rather have the microphones on, but said it "worked out fine" when they were muted on stage with Biden.

"The truth is they're trying to get out of it because [Harris] doesn't want to debate. She's not a good debater,” Trump told media.

Then on Thursday, the Harris team acquiesced, saying it agreed the original rules because it did not want to "jeopardise" the debate.

“Vice-President Harris, a former prosecutor, will be fundamentally disadvantaged by this format, which will serve to shield Donald Trump from direct exchanges with the vice-president. We suspect this is the primary reason for his campaign's insistence on muted microphones," the campaign said.

Tuesday's debate between Kamala Harris and Donald Trump will provide another defining moment in an eventful and tight presidential campaign.

With less than two months until Election Day, it's a high-stakes night for both candidates, where their words and debate style will be put to the test.

The BBC's Courtney Subramanian looks at the strengths and weaknesses of each.

An unusual aspect of this year's debates is that they were agreed upon directly between the candidates and major US networks, side-lining the non-partisan Commission on Presidential Debates, or CPD, that has overseen these events since the 1980s.

CPD, which had intended to organise three debates in September and October, was cut out of the process by Biden and Trump when they agreed to the CNN debate in June.

The campaigns - with Harris now as the Democratic nominee and Trump still the Republican standard-bearer - have so far not agreed on terms for future debates or to work with CPD.

Trump has called for at least two more. He is pushing in particular for a showdown on more friendly turf, moderated by Fox News and with a live audience.

The Harris campaign has said it will evaluate whether or not to do a second debate in October, once tonight's first face-off is over.

On 1 October, the respective vice-presidential picks - JD Vance and Tim Walz - will participate in a single debate on CBS News.

Kayla Epstein

Image source, Getty Images

Philadelphia, Pennsylvania, has both major historic and electoral significance in the US.

Tuesday's presidential debate will take place at the city’s National Constitution Center, a museum and educational space devoted to US democracy.

The city was at the heart of the American Revolution, and the Declaration of Independence was signed in 1776 at the Philadelphia landmark now known as Independence Hall.

Fast forward to 2024 and Pennsylvania is again in the heart of American politics.

The state is heavily contested in this election. Voters in Philadelphia and the surrounding area helped to deliver the state - and the presidency - to Joe Biden in 2020.

This year, Democrats are trying to hang onto Pennsylvania's electoral votes - which will likely prove essential for either candidate to win - and Donald Trump is trying to reclaim it for Republicans.

Here’s what we know about tonight's debate rules:

• The debate is 90 minutes long, with two commercial breaks
• Trump and Harris can’t talk to their staffers during those breaks
• Microphones will be muted for the whole debate, other than when it’s a candidate’s turn to speak
• Props and pre-written notes are not allowed
• But Harris and Trump will be provided a pen and paper, and some water
• There will be no studio audience

• Candidates will have two-minute answers to questions, two-minute rebuttals, and one minute for follow-ups, clarifications, or responses
• A coin flip decided which side of the stage they will stand on and also who will speak last. In this debate, Trump will offer the last two-minute closing statement and Harris will stand stage left

Phil McCausland
Reporting from New York

Image source, Getty Images

Hello and welcome, Kamala Harris and Donald Trump are hours away from squaring off in their first presidential debate.

US broadcaster ABC will host the 90-minute debate at the Philadelphia Constitution Center at 21:00 local time (02:00 BST). You will be able to watch it on ABC News Live, Disney+ and Hulu as well.

You will also be able to watch it by clicking play on BBC's live stream at the top of this page.

The 2024 election cycle has brought much intrigue to the debate stage. President Joe Biden's catastrophic performance at the first presidential debate in June ultimately led to him leaving the race, opening the door to Vice-President Harris's candidacy.

Former President Trump initially said he wouldn’t do the ABC debate because it was agreed to when Biden was his rival.

He pushed for a Fox News debate instead, but Harris stood firm. They both eventually said yes to tonight's debate, but there have been squabbles since that initial agreement.

The two campaigns have bickered for weeks about the debate's rules, though they have finally agreed to parameters similar to those that governed the June debate: mics will be muted unless it is their turn to speak, there will be no studio audience and neither will be allowed props or pre-written notes.