What is the UK Supreme Court?
It is the new highest court in the United Kingdom, acting as a final court of appeal in cases of major public importance.
What that means in practice is that its 12 justices will be the "final arbiters" between citizens and the state, the ultimate check and balance that law is correctly, and fairly, applied.
Is this an entirely new concept?
In the words of Lord Phillips, the first president of the Supreme Court, this is a case of changing the form rather than substance.
The casework that will be dealt with by the Supreme Court is exactly the same as that which came before the justices when they sat as Law Lords in Parliament.
But these senior judges have now left the House of Lords and are therefore independent of Parliament.
This separation brings the United Kingdom into line with many comparable modern states. It means the Supreme Court becomes the final pillar in the constitution: Parliament creates laws, the government and public bodies use those laws - and the courts monitor their application.
Are the justices still Lords?
No. While they retain the title that came with their peerage, they will now be known as the Justices of the Supreme Court. Those who retire may be able to return to the House of Lords.
What kinds of cases will they hear?
The Supreme Court will give the final verdict in all types of cases in the United Kingdom, other than criminal matters in Scotland.
The justices will also offer opinions on major points of law and play a part in the development of law around the world. The justices will hear some cases from the Commonwealth. The justices will also resolve any legal disputes caused by devolution to Scotland, Wales and Northern Ireland.
The court will deal only with cases that the justices consider to be the most important. Their rulings will be limited, as now, to a small number of cases they know will have far-reaching implications.
What has it ruled on in the past?
In 2004, Laws Lords ruled that the government could not hold foreign terrorist suspects without charge indefinitely - a major blow to government security policy. The following year, the Law Lords upheld a ban on hunting with dogs, legislation that had divided Parliament.
In 1993, the Law Lords gave doctors permission to withdraw life-supporting medication from Tony Bland, a football supporter who had suffered irreversible brain damage during the Hillsborough disaster.Q&A: UK Supreme Court
The last case heard by the Law Lords was that of Debbie Purdy, the MS patient, who won her call for greater legal clarity on assisted suicide.
How does the court relate to Europe?
The court has a role in interpreting law passed in the name of the European Union and, separately, ensuring that the British courts take into account rulings from the European Court of Human Rights. Some people whose cases are rejected by the Supreme Court will be able to ask the European Court to intervene where there needs to be more clarity on specific areas of human rights.
How do the justices make their rulings?
There is always an odd number of justices so that there can be a clear majority one way or the other. Justices have each to reach their own conclusions and then write their legal opinion. Cases will typically be heard by five justices, and the most important cases will involve nine.
How do the justices compare with their US namesakes?
The US Supreme Court can strike down a law as unconstitutional - but the UK has no codified, written constitution. If the British justices say that a law is wrong, then the government knows it must eventually bring the matter before MPs for reform. But that doesn't mean the disputed law is torn up before Parliament has had time to think it through.
The most important recent example of this constitutional arrangement was the Law Lords' 2004 decision on indefinite detention of terrorist suspects without charge. The suspects remained in prison while Parliament pushed through legislation to change the system and allow their release and monitoring in the community.
So is there any practical difference between the Lords and the justices?
Although the constitutional differences are subtle, the new justices hope they will now play a greater public role in the life of the nation.
Their court sits in Westminster opposite the Houses of Parliament and is open to the public. It has a cafe and education suite. The Law Lords' judgements were televised, because they were delivered in the House of Lords. But all of the Supreme Court's hearings will be open to the public and, for the first time in British legal history, television cameras will be permanently in court.
How will the justices be appointed?
To become a Supreme Court justice you must have been a senior judge for at least two years or a qualified lawyer for at least 15 years. When there is a vacancy, the justice secretary, also known as the Lord Chancellor, will set up a selection commission. It will consult senior judges who are not putting themselves forward for the court, along with the justice secretary and key figures in Scotland, Wales and Northern Ireland. The justice secretary can accept or reject a nomination. The prime minister then makes a final recommendation to the Queen, who makes the appointment.
Does that mean there will be a lot of courtroom drama?
The Supreme Court job is to examine the finer parts of the law and its application. It is not the kind of thing that lends itself to dramatic courtroom flourishes.
That doesn't mean the cases will not be dramatic in their own ways. Their first case in October concerns how the government freezes the assets of terrorism suspects. A future case involves a former MI5 officer who wants to publish his memoirs.
How much does the Supreme Court cost?
There has been a £59m programme to renovate the Middlesex Guildhall and turn it into the Supreme Court. A further £18m has been spent on new courts for the criminal cases moved from the building to another location. The Ministry of Justice says the Supreme Court will cost about £13.5m a year to run.