The UK Parliament has backed British participation in air strikes against Islamic State extremists in Iraq.
After a seven-hour debate, MPs voted for military action by 524 votes to 43.
The Conservatives, Lib Dems and Labour leaderships all backed air strikes although some MPs expressed concerns about where it would lead and the prospect of future engagement in Syria.
The BBC's political editor Nick Robinson said RAF planes could be called into action as early as Sunday.
Speaking after the vote, Defence Secretary Michael Fallon said a long campaign lay ahead and there would not be a "series of immediate hits".
He told the BBC the priority would be to stop the "slaughter of civilians" in Iraq and the UK and its allies would continue to be guided by Iraqi and Kurdish intelligence in identifying targets.
In other developments:
- The Pentagon said four IS tanks had been destroyed during the latest US raids in Syria
- Denmark and Belgium say they will contribute seven and six fighter planes respectively to the international coalition. The UK is contributing six Tornado strike aircraft.
- Speaking in a separate debate in the House of Lords, the Archbishop of Canterbury, Justin Welby, supported action but called for "an ideological and religious" solution rather than a military one.
- The daughter of murdered British aid worker David Haines backs RAF air strikes
Analysis by BBC diplomatic correspondent Jonathan Marcus
Six additional aircraft - RAF Tornados operating out of Cyprus - is hardly a massive deployment of air power, but the British role is nonetheless significant - both politically and militarily.
The key success of the US-led coalition is to have so many Arab states as active participants.
But western military contributions are also vital; with France, Australia and the Netherlands already on board, Britain adds another weighty player.
The RAF Tornados bring very advanced targeting capabilities but their significance to the ever growing coalition is also about sustainability.
So far - despite much misleading commentary in the press - this is a relatively low level air campaign.
The numbers of aircraft involved is not huge. But the problem for the coalition is to sustain their activities over time.
This campaign against Islamic State could potentially go on for years.
Each country's contribution (leaving aside the Americans) may be small, but together they make up a force that could continue operations almost indefinitely.
Some 23 Labour MPs voted against air strikes, as did six Conservatives, one Liberal Democrat, two Plaid Cymru MPs and five Scottish National Party MPs.
They were joined in the no lobby by Green MP Caroline Lucas, three Social Democratic and Labour party MPs and Respect MP George Galloway. Two MPs acted as no tellers during the vote, Labour's Jeremy Corbyn and the SNP's Pete Wishart.
Earlier, Prime Minister David Cameron told MPs that intervention at the request of the Iraqi government was "morally justified" to combat a "brutal terrorist organisation" and was clearly lawful.
He said Britain had a clear "duty" to join the campaign, saying IS was a direct threat to the UK and he was not prepared to "subcontract" the protection of British streets from terrorism to other countries' air forces.
He won support from Labour leader Ed Miliband who said inaction would lead to "more killing" in Iraq, large swathes of which are controlled by Islamic State.
Mr Cameron also said there was a "strong case" for UK military intervention in Syria, where the US and its Arab allies are engaged in aerial bombardment of IS positions.
The PM said he believed military action there would be lawful on the grounds of intervening to prevent a humanitarian catastrophe, and of protecting Iraq from attacks being launched from Syria.
But he acknowledged there was no consensus for such a move among MPs.
The government has said it would seek separate Parliamentary approval for the extension of air strikes to Syria but reserved the right to act without consulting MPs in the event of a humanitarian emergency.
Meanwhile, shadow education minister Rushanara Ali, the MP for Bethnal Green and Bow, earlier resigned from the party's front bench in order to abstain in the Iraq vote.
Labour MP Iain McKenzie was sacked as an aide to shadow defence secretary Vernon Coaker for failing to back air strikes.
Liberal Democrat leader Nick Clegg said it was "impossible to reason with" Islamic State and the UK should not be "paralysed" by the legacy of the 2003 Iraq War.
And Mr Miliband - who a year ago forced the prime minister to abandon plans for air strikes against the Syrian regime by inflicting a Commons revolt on the issue - said the UK "cannot simply stand by".
Speaking after the vote, Labour MP John McDonnell - who voted against air strikes - said the previous intervention in Iraq was one of the causes of the emergence of the jihadist movement.
"We seem to be making the same mistakes without any alternative strategy," he told BBC News.
The US began a series of air strikes in Iraq last month, and on Monday it began attacks on targets in Syria. Jets from Saudi Arabia and the United Arab Emirates have joined US forces in the attacks, and the US says more than 40 countries have offered to join the anti-IS coalition.