"When it came to computer crimes and the like, the government was implicated," Mueller says, when asked to describe how Russia allegedly interfered in the US election.

He says it is "accurate" that a top aide to Trump campaign manager Paul Manafort - Rick Gates - shared US polling data with a Russian operative.

Mueller says the Russian government thought it would benefit from the election of Trump, who he accidentally called "Trimp" before correcting himself.

Collins and Mueller get into a back-and-forth over exact definitions of collusion vs conspiracy.

"Although your report states collusion is not a specific offence... conspiracy is," Collins says. "In the colloquial context are collusion and conspiracy essentially synonymous terms?"

Mueller replies: "No."

"You wrote collusion is largely synonymous with conspiracy," Collins responds.

"Are you sitting here testifying something different than what your report states?"

Mueller asks for the specific citation, but Collins responds: "I just stated your report back to you. You said collusion and conspiracy were not synonymous terms... Now you said you chose your words carefully. Are you contradicting your report right now?"

Mueller answers, after re-reading, that he'll agree with the report.

Republican ranking member Doug Collins begins his questioning.

Collins asks if the investigation was ever hindered.

"No," Mueller replies.

The president never agreed to be interviewed by Mueller and his team.

But last year, he gave written answers to a list of questions about Russian interference.

Read the full story here.

"Is it correct that if you had concluded that the president committed the crime of obstruction, you could not publicly state that in the report or here today?" asks Judiciary chairman Jerry Nadler.

Rules mean that "you would not indict", Mueller says, clearing his throat.

He says that he could not state that Trump had committed a crime, even if it was his opinion.

He said that despite over a year of negotiations, Trump refused to sit for an interview with Mueller.

"Your report did not conclude that he [President Donald Trump] did not commit obstruction of justice, is that correct?" asks Democrat Jerry Nadler.

"Correct," Mueller responds.

"Did you totally exonerate the president?"

"No," Mueller flatly states.

"The president was not exculpated for the acts he allegedly committed," Mueller explains.

As Mueller entered the room, a shouting protester was removed by security.

It's unclear what he was yelling.

Image source, Getty Images

Image source, Reuters

Mueller emphasises that Russian meddling efforts are a serious concern.

"Over the course of my career, I’ve seen a number of challenges to our democracy," he says.

"The Russian government’s effort to interfere in our election is among the most serious. As I said on May 29, this deserves the attention of every American."

"I do not intend to summarize or describe the results of our work in a different way in the course of my testimony today," Mueller notes.

"As I said on May 29: the report is my testimony. And I will stay within that text."

Mueller addresses obstruction of justice: "Obstruction of justice strikes at the core of the government effort to find the truth and hold wrongdoers accountable."

He says: "We investigated a series of actions by the president toward the investigation. Based on Justice Department policies and principles of fairness we decided we would not make a determination whether Mr Trump committed a crime."

He added that his testimony today would be "limited", and called it highly unusual for a prosecutor to answer questions about an investigation such as this.

Image source, Getty Images

Mueller, who was appointed as special counsel in May 2017, says he saw the job as vital to US democracy

"I undertook that role because I believed it was of paramount interest to our nation to determine if a foreign adversary attempted to influence our election."

He says it was necessary that the public have confidence in his findings.

"My staff and I carried out this assignment with that critical objective in mind, to work quietly, thoroughly and with integrity so that the public would have full confidence in the outcome," he says.

"Our team did not leak or take other actions that would compromise the integrity of our work," he adds.

He also speaks of having charged more than 30 people - including Russian intelligence officers - with committing federal crimes.

"For two years Americans were told what to expect and what to believe," says Republican Doug Collins, but today they will hear the evidence for themselves.

He says that Mueller found evidence that Russia attempted to interfere with the US election, but said Mueller did not conclude that Trump or his team attempted to collude with Russia.

"The president's attitude towards the investigation was understandably negative," he says, but he did not use his powers to shut down the investigation.

That's because Trump knew he was innocent of any charges, says Collins.

Nadler summarises volume two of Mueller's report, saying it "walks us through 10 separate incidents of possible obstruction of justice where, in your words, President Trump attempted to exert undue influence over your investigation".

Those instances include:

• Public attacks on the investigation
• Non-public efforts to control it
• Encouraging witnesses not to co-operate
• Ordering White House counsel to remove Mueller
• Ordering former campaign manager to convince recused Attorney General to limit Mueller inquiry

Judiciary chairman Jerry Nadler has begun by praising Mueller's integrity - saying his career "is a model of responsibility" - before getting into the possible instances of obstruction of justice by President Trump.

"Although department policy barred you from indicting the President for this conduct, you made clear that he is not exonerated," Nadler says.

"Any other person who acted this way would have been charged with a crime. And in this nation, not even the President is above the law."

Aaron Zebley is alongside Mueller today and will serve as his counsel during the day's double-feature hearings.

Earlier this week, Mueller requested that Zebley be sworn in as a witness to testify on his behalf, but the plan was ultimately scrapped.

Since he is not sworn in, he is prohibited from speaking directly to committee members.

Republican Congressman Doug Collins of Georgia said Zebley has not assured the committee that he will not "waste time" by speaking to them directly.

Zebley has been a close Mueller confidant for years. He worked alongside him during the 22-month Trump-Russia probe, served as his chief of staff when Mueller was FBI director and followed him into private practice at the WilmerHale law firm.

Mueller has just walked into the committee room.

Opening statements are now beginning.

Congressman Jerry Nadler is starting now.

Robert Mueller is set to face questions from two congressional committees about his report on nearly two years of investigation into the Trump campaign and Russian meddling.

The BBC's Anthony Zurcher tells us what to expect - and gives us a refresher on how we got here.

The New York Times podcast The Daily pointed to how few Americans still follow Mueller intrigue months after his redacted report was made public.

Host Michael Barbaro described today's hearing as the "denouement anti-climax" of the probe, since Americans have already had time to digest what Mueller has to say.

During a news conference in late May, Mr Mueller said that if called to testify, he would not discuss anything beyond his report's findings.

Reporter Michael Schmidt (who describes himself as an "obstructionist" - one specialising in the obstruction of justice aspect, as opposed to his colleague Michael Mazzetti who is a "collusionist") said Democrats will try to force Mueller to say that Trump would have been charged if he were not a sitting president.

Department of Justice guidelines say that a president cannot be charged with a crime.

You probably don't have time to get through all 448 pages of Mueller's report before the questions begin - but we've got you covered.

Pew Research Center data shows that nearly two-thirds of Americans, and for the first time a majority of Republicans, believe Mueller conducted a fair investigation.

During the almost two-year investigation, Republican voters mostly expressed negative views of the probe.

In January, only 39% of Republicans said they had confidence in Mueller's investigation, compared to about to 60% today. One-third of Americans say they still do not have full confidence in the investigation.

According to the survey, only 46% of Americans believe that the Trump government is making a serious effort to prevent Russia from future electoral interference.

Image source, Pew Research Center