The trial of Radovan Karadzic at the UN's International Criminal Tribunal for the former Yugoslavia (ICTY) in The Hague opened on 26 October 2009.
The former Bosnian Serb leader is accused of having direct responsibility for the worst atrocities of the Bosnian war - described as the worst crimes committed in Europe since World War II.
What are the charges against Mr Karadzic?
He faces 11 counts of genocide, war crimes, crimes against humanity and other atrocities in the Bosnian war of the 1990s.
The trial is the ICTY's most high-profile case since that of Slobodan Milosevic
The charges relate to several events, including his alleged part in the shelling of Sarajevo during the city's 44-month siege, in which some 12,000 civilians died.
He is also alleged to have been behind the massacre of more than 7,000 Bosniak (Bosnian Muslim) men and youths in Srebrenica and of shelling towns in the region as part of a campaign to drive Bosniaks and Bosnian Croats out of areas claimed by Bosnian Serb forces.
He is accused of targeting Bosniak and Bosnian Croat political leaders, intellectuals and professionals.
He is also charged with unlawfully deporting and transferring civilians because of national or religious identity, and of destroying homes, businesses and sacred sites.
And he is said to have used 284 UN peacekeepers as human shields in May and June 1995.
How long will the trial take?
It is difficult to know long Mr Karadzic's trial will last, but the court estimates proceedings will not be completed before early 2012.
The 64-year-old, who is defending himself, tried to delay the trial's 26 October start date, saying he had not had enough time to prepare.
The court's judges asked the prosecution to abbreviate the scale of the trial, which Mr Karadzic said depended on more than a million pages of testimony.
The court wants to prevent a repeat of the trial of Slobodan Milosevic for war crimes and crimes against humanity. The former Yugoslav president spun his case out through repeated delaying tactics, until he died suddenly in 2006.
His death was a blow to prosecutors, who regarded him as the man ultimately responsible for the bloodshed that ripped Yugoslavia apart.
How did Mr Karadzic end up at The Hague?
Mr Karadzic was jointly indicted in 1995 along with the Bosnian Serb military leader, Ratko Mladic, for alleged war crimes they committed during the 1992-95 war.
He was obliged to step down as president of his party in 1996 as the West threatened sanctions against the Bosnian Serb government, and later went into hiding.
He was found living disguised and under a false name in Belgrade in July 2008, and arrested.
He was held initially at the War Crimes Court in Belgrade. A Serbian judge ruled he should be handed over to the ICTY, in line with Serbia's law on co-operation with the court.
What is Mr Karadzic's position?
The former leader made his first appearance before the war crimes tribunal on 31 July 2008, when he announced his intention to represent himself and complained that Judge Alphons Orie was biased against him.
He refused to enter a plea at a second appearance on 29 August 2008 before a new presiding judge, Iain Bonomy.
The court entered not guilty pleas for all counts on his behalf, according to its rules.
Mr Karadzic has since filed several requests to delay his trial, saying he needs more time to study a million pages of prosecution evidence and the statements of hundreds of witnesses.
Days before his trial was due to start on 26 October, he wrote a letter to the court saying he would not be appearing as he had not had sufficient time to prepare.
He subsequently did not attend the first day, with the judge asking him to appear on the second when the prosecution is due to give its opening argument. His legal adviser said he would not attend.
He is being held at the UN detention unit in the seaside resort of Scheveningen, just outside The Hague.
How does this trial compare to others at the ICTY?
Prosecutors are scheduled to make opening statements over the first two days of the case and will then reportedly take about a year to present their case.
Mr Karadzic will then be given the same amount of time to mount his defence.
The trial is the ICTY's most high-profile case since that of Slobodan Milosevic. Mr Karadzic could be the tribunal's first defendant successfully prosecuted for genocide. Although army leader Radislav Krstic was convicted of genocide at the ICTY in 2001, the verdict was overturned on appeal in 2004.
The tribunal cannot impose the death penalty; its maximum sentence is life imprisonment.
The longest sentences passed to date were life - reduced to 40 years on appeal - for Bosnian Serb Milomir Stakic, the former mayor of Prijedor in northern Bosnia, and 40 years for Bosnian Serb prison camp guard Goran Jelisic.
The ICTY is an ad hoc tribunal established by the UN Security Council that is expected to wrap up its work in the next few years.
The latest estimates suggest all but four of the ICTY's trials will conclude in 2010, three more in early 2011, and the final trial - that of Mr Karadzic - in early 2012.
Two fugitives remain at large: the Bosnian Serb military leader Ratko Mladic and Goran Hadzic, a Croatian Serb who is wanted for war crimes.
The tribunal may not try suspects in absentia. If the remaining two fugitives are caught, it is presumed the ICTY's closure could be delayed.
What is the UN detention unit like?
It was built in the mid-1990s within the confines of an existing Dutch government prison. Currently it is holding a number of other detainees indicted over the 1990s wars in former Yugoslavia.
Mr Karadzic is being held in a cell like this at the UN detention unit
Each inmate gets a single cell, measuring 15 sq m (170 sq ft), complete with shower, toilet, washbasin, desk and chair.
They also get television in five languages, as well as satellite TV in their own tongue.
Inmates who are representing themselves also get an additional "archive cell", a telephone and a computer to help them prepare their case.
There are games rooms for darts, table tennis and board games, and lessons are offered in art and languages. A prison library is also provided, along with a courtyard for exercise.
A doctor is on permanent standby, along with a nurse and a psychologist, and several Dutch hospitals - among the world's most advanced - are within minutes of the prison gates.
There is also a room, the so-called Comfort Room, which is closed off from the rest of the prison visiting area and its ubiquitous cameras. It contains a bed and is reserved for conjugal visits.
During his first appearance in court, Mr Karadzic complained about the circumstances of his arrest, saying he was held incommunicado for three days.
But he said he had no complaints about his treatment since his arrival in The Hague. "I've been in worse places," he said.