Former IMF chief Dominique Strauss-Kahn has gone on trial in France accused of pimping prostitutes.
The one-time political high-flyer had been tipped to become French president before a New York hotel maid accused him of sexual assault in 2011.
Strauss-Kahn, 65, who settled a US civil case with chambermaid Nafissatou Diallo after criminal charges were dropped, risks up to 10 years in jail and a fine of up to €1.5m if convicted in the trial in Lille.
The court rejected a prosecutor's request for the trial to be held behind closed doors to protect the identity of prostitutes who are due to testify about their encounters with Strauss-Kahn and others.
Investigators, who sent Strauss-Kahn to trial with 13 others, argue he knew he was dealing with prostitutes when taking part in sex parties in Paris, Lille and Washington from 2008 to 2011, a judicial source told Reuters.
He is charged with "procuring with aggravating circumstances".
Prosecutors say the charge of procuring, or pimping, is applicable because, under the French legal definition, it extends to any activity seen as facilitating prostitution.
In Strauss-Kahn's case, judicial investigators allege he allowed his rented apartment to be used for sex parties involving prostitutes and that he was involved in organising them.
Defence lawyers for Strauss-Kahn have flatly dismissed those allegations, arguing he never made a secret of his penchant for sex parties but was unaware the women present were prostitutes and did not play any pivotal organisational role.
Strauss-Kahn, wearing a black suit, white shirt and tie, was driven into the courthouse in a dark-windowedcar. He was accompanied by his three defence lawyers.
The matter has come to be known as the Carlton Affair, named after a hotel in Lille that is at the centre of police investigations into a broader sex ring.
Strauss-Kahn, French finance minister in a boom-time Socialist government in the late 1990s, became one of the world's most influential decision-makers in 2007 as head of the IMF.
That high-flying career ended in May 2011 when the world witnessed live TV images of the then IMF chief being escorted handcuffed into custody in New York after the accusations of Sofitel room cleaner Diallo.
Strauss-Kahn, who had been preparing to run for French president and was enjoying a runaway lead in opinion polls ahead of the 2012 contest, resigned from the IMF.
The fall from grace destroyed his political ambitions, leaving the way free for Francois Hollande.
Since returning to France, Strauss-Kahn has separated from his celebrity journalist wife, Anne Sinclair, met a new partner and pursued a career in private-sector investment.
The trial is expected to run for at least three weeks, a court official said.