First US presidential debate: Obama v Romney

Welcome to BBC's live page of the first presidential debate between President Barack Obama and Republican challenger Mitt Romney. We'll bring you all the insights from our correspondents at the event in Denver, as well as a selection of your e-mails and tweets.

The head-to-head begins at 19:00 local time (02:00 BST) and runs uninterrupted for 90 minutes, focusing on domestic policy, including the economy and healthcare. It is the first of three presidential debates and a vice-presidential one before the election on 6 November.

If the US presidential campaign and the candidates are relatively new to you, here's a quick look at where each stands on the key issues - and our full election coverage.

And here's our candidates...

No, you haven't been transported to an alternate reality: two University of Denver students - Zach Gonzales (left) and Dia Mohamed - stood in earlier for the former Massachusetts governor and current US president during a rehearsal and camera test.

Recent polling suggests Obama has maintained a slight lead nationally as well as in several key election states (our poll tracker has the big picture). A crash-and-burn by either candidate tonight could really hurt his approval rating.

Pundits say Obama must ensure he doesn't damage his buoyant likeability ratings, while bringing the attack to Romney. The New York Times has reported that aides are encouraging Obama to use humour and his wide smile, and to avoid coming across as smug.

Romney has reportedly been equipped with an arsenal of "zingers" - the one-line put-downs that leave spin-doctors drooling and YouTube creaking.

With 15 minutes to go, the audience have taken their seats and are being given a stern warning about keeping their phones off and refraining from cheering and applause throughout the debate.

But do presidential debates matter? BBC North America editor Mark Mardell says that while these clashes may not change minds, they do make for better informed voters.

The moderator for this evening, Jim Lehrer, has run a presidential debate 12 times in his career. His day job is executive editor of PBS Newshour, a nightly US news programme. A former CNN anchor called Lehrer the "dean of moderators", but others suggest his style is too gloves-on.

The New York Times previews the debate through numbers or statistics likely to be used to buttress arguments or provide rhetorical flourish this evening.

The format for tonight's debate is designed to get a bit more discussion going - the 90 minutes will be split into six 15-minute segements, each themed around a policy issue.

The two men have rarely met in person in the past few years - and according to Politico, Obama is no admirer of Romney, regarding the former governor as "a political shape-shifter".

Jim Lehrer's final request for silence before the debate is being immaculately observed - in the media room as well as in the debate hall itself.

And the two big beasts of the American political jungle stride on stage, all smiles. Obama claps Romney on the arm. Mr Obama in a blue tie - Mr Romney in red. They make quick waves to the audience and arrive back at the podium.

The first question is - unsurprisingly - about jobs.

Romney cracks a joke, saying it is very romantic that Obama is spending his wedding anniversary on stage with the Republican. Obama laughs.

Looking his rival in the eye, Mitt Romney denies Obama's claim that he has a plan to cut taxes, says middle-income Americans have been "buried" and "crushed".

Romney says he wants "tax relief" - arguing that Obama's policies have hit the poor the worst.

Expressive with his hands, Romney says he likes coal and wants to bring in a disputed oil pipeline from Canada (the Keystone XL project has been a bone of contention during Obama's first term). Says Obama's characterisation of Romney's policies are "simply not accurate".

Back to taxes - Obama repeats his line that Romney will bring in a $5.4 trillion tax cut and says Romney hasn't been clear about what the loopholes in the tax system he would close. Romney is now fighting back firmly against Obama's claims.

Obama is shaking his head at Romney's claim that six studies have contradicted the president's characterisation of the Republican's economic plan. "For me this is about getting jobs for the American people," emphasises Romney.

Romney adopts a respectful tone, referring to Obama as "Mr President".

Obama says that Romney's tax plan is "mad". "Math, common sense and our history shows that's not a recipe for job growth". Says it's the same Republican sales pitch that led to the Great Depression.

Social media website Tumblr is live giffing during the presidential debate. If you want to know what this is all about, click here to see what is being created.

Romney ends the first segment by again emphatically denying that he is planning a $5 trillion tax cut.

A light moment, as Romney refers to the president's signature healthcare reform as "Obamacare", adds that he uses that term "with all due respect". Obama says: "I like it."

Romney spells out his test for dropping government programmes: "Is it so essential that we need to borrow from China to pay for it?"

Obama cites Romney as saying during the Republican primaries that he would not exchange $10 of government cuts for $1 of tax revenue, calls that an "unbalanced approach".

Romney hits Obama hard on the economy, saying he's had four years to fix it. Obama says Romney has ruled out extra tax revenue. Romney interrupts and says "absolutely", before going on to riff about how tax increases harm the economy.

Romney cites Spain's percentage of government spending - and brings up the spectre of that country's economy: "We don't want to become Spain."

A fact-check from NYT: "It's not true that Obama added as much to the federal debt as all the prior presidents combined."

Obama attacks "corporate welfare" - saying Exxon Mobil doesn't need tax breaks - and neither do the owners of private jets.

Former private equity chief Romney brings up what his campaign sees as his unique selling point as he takes a swipe at Obama: "I've been in business for 25 years - I have no idea what you're talking about."

Obama looks tired, fails to tell a story, has no spark, gathers a bunch of points together and spools them out. So far, a dismal performance. A car crash. Fortunate for Dems that very few debates change campaigns in any way.

Mitt Romney attacks Obama's policies on green energy, mentioning Solyndra, a high-profile solar firm that failed after receiving major government subsidies.

Romney and Obama may look like long-lost buddies in this picture, but they're not.

Obama says that if you repeal Obamacare (he's owning the name now) seniors will lose out and insurance companies will gain.

I'm in Charleston, South Carolina - a solidly Republican state, at a Republican watch party. There are 200 people in a cinema heckling President Obama and cheering Mitt Romney, calling out "liar" when Obama talked about energy. When Obama talks about his family story the audience say: "Wake me up when you're done".

Obama makes a case for regulation of Wall Street - asking ironically if anybody thinks the cause of the 2008 financial crisis was too much red tape.

Romney hits Obama's healthcare law hard - bad for small business, too much time spent on the law during his first two years - and not enough on jobs.

Obama cuts off the moderator as points out his two minutes are up, saying: "I had five seconds before you interrupted me". Softens the sharp comeback with a smile.

Obama says its more than businesses affected by his healthcare law - argues it will prevent middle-class families from bankruptcy and stop health insurers "jerking" customers around.

Obama tries to keep the floor, demanding his extra five seconds on healthcare - and uses it to bring up Romney's Massachusetts health reforms. But he stutters slightly and soon has to end his answer. Did he make the most of what was clearly a pre-planned attack? Romney pivots quickly back to why he thinks Americans don't want Obamacare.

"The private market and individual responsibiity always work best," says Romney, as he attacks the Obama healthcare reform.

PolitiFact fact-check: Is Romney plan for future Medicare a voucher system? Mostly True

Romney is punching through the heartless-corporate-suit caricature and comes across as competent and as normal as presidential candidates get.

Romney says his Massachusetts healthcare scheme - which was the model for Obama's own reform - was fine as a state-level plan, but not as a national one.

Obama suggests Romney is keeping his plans "secret", as he suggests his rival is being vague on the specifics of his proposals.

Another suggestion from Obama that Romney's plans lack specifics. On education, the president says that Romney's proposal "wasn't very detailed - this seems to be a trend".

Romney says that Obama invested $90bn on green energy, which would have hired two million teachers. Says that government mustn't pick winners and losers in the private sector.

Romney: "The reason I'm in this race is that there are people who are really hurting in this country... Republicans and Democrats both love America - but we need leadership in Washington."

In the world of Twitter, one of the big emerging themes from the debate that is now in the top five trending terms worldwide is Romney's remark that he loves Big Bird - apparent concern that Romney might fire Big Bird from Sesame Street.

How to end partisan gridlock? Romney says he's done it in Massachusetts and he will sit down on day one with Democrats. Obama says he's going to have a busy day, what with repealing Obamacare and then sitting down with its Democratic supporters.

Obama lost the coin toss and so he makes the first closing statement.

Obama says America's strength is its people, "their genius, their grit, their determination", says it is important that everybody has a fair shot, everybody is playing by the same rules.

Romney says he'll get incomes up again, that he'll create 12 million new jobs, says that if Obama is re-elected the US will see a $716bn cut to Medicare, says Obama will bring drastic cuts to the military.

And it's over. Obama's wife Michelle joins him on stage, so does Romney's family, they're all talking together, it looks like a parent-teachers' council meeting.

Obama's left the stage but Romney lingers there with his family, giving the thumbs up to the crowd, before departing.

CNN breaks down the speaking time for the two candidates during the debate: Obama spoke for 45 minutes and 50 seconds, Romney for 38 minutes and 32 seconds.

As the debate comes to a close, Obama and Romney's surrogates are in the media centre spinning fervently for their candidate. The next presidential debate will be on 16 October, but before that Joe Biden and Paul Ryan will joust in the only vice-presidential debate, on 11 October.

What was true and what was a distortion? Factcheckers at the New York Times, Washington Post and PolitiFact have been refereeing the candidates' claims.

Romney was animated, in command of his information, over-riding the moderator and interrupting the president. He seemed to be in charge and enjoying the scrap. On the other hand, President Obama started out looking very nervous, and although he warmed up got into his stride, he ended up giving overly long, mini-lectures rather than engaging and arguing. He seemed unwilling to actually debate with his opponent, and missed a few obvious openings when he should have challenged.

That's it for our coverage of the first presidential debate. Join us for the next head-to-head between Obama and Romney on 16 October in Hempstead, New York. It's going to be a town-hall style foreign policy forum and CNN's Candy Crowley will moderate. Thanks for joining us!