The US Supreme Court has ruled that a ban on handguns in Washington DC is unconstitutional, and that Americans have the right to own guns for personal use. It was the first time the court had considered the issue in almost 70 years, and the ruling could have wider implications.
What was the case before the Supreme Court?
The nine justices were hearing a challenge to one of the toughest gun laws in the nation - a virtual ban on private handgun ownership in the city of Washington DC, passed in 1976.
The case was brought in the name of security guard Dick Heller, a District of Columbia resident who carries a gun at work and wants to be able to keep it at home for self-defence. He and his supporters argued that the ban violated the rights of DC citizens.
City officials said the ban was necessary to keep gun violence down, and argued that the Second Amendment to the US Constitution protected a right tied to service in a militia, not an individual's right to bear arms.
The challenge to the ban was initially rejected, but a federal appeals court later overturned that judgement.
As a result, District of Columbia vs Heller came before the Supreme Court, the first time it has ruled on the Second Amendment since 1939.
Why is the case so important?
At the heart of the case is the Supreme Court justices' interpretation of the Second Amendment.
Added in 1791, it states: "A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed."
The definitive meaning of the sentence, with its odd punctuation and phraseology, has been the subject of much scholarly debate and political argument over the years.
The judges have decided that the Second Amendment guarantees the right of individuals to bear arms, rather than just protecting the collective right of states to maintain militias.
The ruling could have an impact on gun-control laws elsewhere in the US - although 44 states have constitutional provisions that protect the right to individual gun ownership.
What kind of impact is the ruling likely to have?
In DC, as well as judging the ban on handguns unconstitutional, the Supreme Court also struck down its requirement under the 1976 law that rifles and shotguns should be kept unloaded and dismantled or with trigger locks fitted.
However, firearms kept in the district will still have to be registered.
Elsewhere, the National Rifle Association plans to file lawsuits challenging restrictions on handgun ownership in cities including San Francisco and Chicago, based on the ruling.
It remains to be seen whether the fears of gun-control advocates that a ruling against the DC ban could seriously undermine other restrictions on private gun ownership are justified.
But Justice Antonin Scalia, giving the majority opinion, wrote that nothing in the court's ruling should "cast doubt on long-standing prohibitions on the possession of firearms by felons or the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings".
Other laws restrict the sale of machine guns and provide for instant background checks on those buying guns.
What were the arguments against the DC handgun ban?
Opponents said it was an unconstitutional ban on an individual liberty protected by the Bill of Rights.
They also argued that there was no clear evidence that DC's gun laws were effective, pointing to the fact that nearly 80% of DC's 181 murders in 2007 were committed with guns.
This demonstrates that criminals have little trouble getting hold of them, they said, at the same time as the ban prevents those who follow the law from protecting themselves.
Alan Gura, the lead lawyer for Mr Heller, said the laws had "accomplished nothing except to prevent law-abiding citizens from exercising their constitutional right to keep and bear arms".
What were the arguments for maintaining the ban?
The city argued that the Second Amendment did not refer to an individual right, but was intended to allow states to keep their own armed forces.
DC officials said the ban made the capital safer because, although illegal handguns still made their way on to the capital's streets, there were fewer legally owned ones to be stolen or used in domestic incidents.
They warned that gun violence could increase without the law, leading to more deaths.
"Whatever right the Second Amendment guarantees, it does not require the district to stand by while its citizens die," the city wrote in its petition to the Supreme Court last year.
Where do the candidates for the White House stand?
Senator John McCain, the presumptive Republican nominee to run in November's election, was among a majority in Congress to supporting the challenge to the ban.
After the ruling, he said: "I applaud this decision... Unlike the elitist view that believes Americans cling to guns out of bitterness, today's ruling recognises that gun ownership is a fundamental right - sacred, just as the right to free speech and assembly."
His Democratic rival, Senator Barack Obama, did not sign the brief presented to the court.
He has said he believes the Second Amendment protects an individual's right to own a gun but that the federal government should be able to impose restrictions.
Responding to the judgment, Mr Obama pointed out that Justice Scalia had, while ruling that the DC ban went too far, acknowledged that the right to bear arms is "not absolute and subject to reasonable regulations".
The gun rights lobby is a powerful force in American politics and could potentially use the issue to galvanise conservative voters in November's election.
What is the Bush administration's position?
Following the ruling, White House spokeswoman Dana Perino said President George W Bush strongly agreed with court's "historic decision" that the Second Amendment protects the individual's right to bear arms.
"This has been the administration's long-held view," she said, adding that Mr Bush was also pleased the DC handgun ban had been ruled to violate that right.
In 2001, then-Attorney General John Ashcroft backed the interpretation that the Second Amendment protects individual rights - a reversal of long-standing justice department policy.
But Solicitor General Paul Clement wrote in a brief to the Supreme Court that while the amendment preserved an individual right, he believed the appeals court had been wrong categorically to rule DC's handgun ban unconstitutional.
"If adopted by this court, such an analysis could cast doubt on the constitutionality of existing federal legislation prohibiting the possession of certain firearms, including machine guns," he wrote.
Vice-President Dick Cheney was among a number of gun rights supporters who criticised Mr Clement's position - and went so far as to sign a friend-of-the-court brief rejecting the administration's view on the DC ban, as expressed by Mr Clement.
Why does gun ownership matter to Americans?
Some observers relate the importance of firearms to the American psyche to the country's relatively recent history as a frontier nation, peopled by settlers who had to be largely self-sufficient.
Many Americans see their right to gun ownership as an essential personal liberty guaranteed by the Bill of Rights - and it is one they are determined to keep.
That attitude is supported by the National Rifle Association (NRA), a powerful gun rights lobby.
Surveys estimate that there are now 90 guns for every 100 citizens in the US, making it one of the most heavily-armed nations in the world - although that figure covers people who own multiple guns, and many Americans do not possess firearms.
Those who support gun control argue that easy access to guns makes it more likely that they will be used and call for greater restrictions on their sale.
Firearms, including handguns, are used in two-thirds of murders and about 42% of robberies committed in the US, according to statistics from the FBI.