At the centre of the case is an alleged attempt over several years by friends, associates and employees to "abuse the mental weakness" of France's wealthiest woman, the L'Oreal chief shareholder, Liliane Bettencourt, who is now 92.
The 10 defendants include Eric Woerth, campaign treasurer to Nicolas Sarkozy in 2007 and a former budget minister. He is accused of "receiving" at least 150,000 euros ($228,000) in cash for Mr Sarkozy's presidential campaign, knowing the money to have been extracted from the ailing billionairess.
He denies the charge.
The former president was, for a time, also formally accused of "abusing" Ms Bettencourt's weakness of mind by pestering her for illegal campaign contributions.
The accusations against him were dropped in 2013 for lack of clear evidence.
The principal defendant is Francois-Marie Banier, 67, a gay socialite and photographer, who was a friend and frequent companion of the billionairess and her husband for many years.
The Bettencourt affair unfolds
The affair began in late 2007 when Mr Banier was accused by Ms Bettencourt's daughter of extracting over 1 billion euros in cash, savings accounts and art works from her mother.
In settlement of a separate civil claim, he has already returned several hundred millions of euros in art works and other "gifts".
Mr Banier remains accused of defrauding the elderly woman of 400m euros. His boyfriend, Martin d'Orgeval, 41, is accused of taking art works worth 5m euros.
Their lawyers will argue that Ms Bettencourt gave them the money and art works willingly, long before there were doubts about her mental condition.
As chief shareholder of L'Oreal, she was worth 30b euros at the time.
Mr Banier said in written testimony: "She gave me a considerable amount but the richest woman in France is free to do what she wants with her money. She wanted to free me to concentrate on my literary and photographic work."
Mr Banier has presented character testimonials in writing from a series of high-profile friends, including the actress Vanessa Paradis and the fashion mogul Pierre Berge.
The other principal accused is Ms Bettencourt's former financial adviser, Patrice de Maistre, 65, who is charged with taking advantage of his employer's weakness to embezzle 12m euros.
Both he and Mr Banier are also accused of money-laundering - the charge to which they raised procedural and constitutional objections yesterday.
At the start of yesterday's hearing, the court was told that Alain Thurin, 54, a relatively minor defendant, had attempted to commit suicide on Sunday. He was said to be fighting for his life.
Mr Thurin, Ms Bettencourt's former nurse, is accused of persuading her to open a 10m euros savings account in his name. He denies the charge and insists that she created the account without his knowledge.
Defence lawyers are expected to try to turn the case into a de facto trial of Ms Bettencourt's daughter, Francoise Bettencourt-Meyers. They will claim that the whole affair is a mother-daughter feud which spun out of control.
In particular, they will challenge the admissibility of "bugging" evidence against several of the accused, including Mr Sarkozy's ally Mr Woerth.
This evidence came from a listening device installed in a sitting room at Ms Bettencourt's mansion near Paris by her butler - allegedly at her daughter's instigation.
Defence lawyers will also object to the absence on medical grounds of one of the chief prosecution witnesses, Ms Bettencourt's former accountant, Claire Thibout.
Sarkozy drawn into political scandal
It was Ms Thibout who turned the affair into a political scandal in 2010 by telling police, among other things, that Mr Woerth and Mr Sarkozy had received envelopes stuffed with Bettencourt family cash.
Ms Thibout is now under formal legal investigation herself for alleged perjury. This separate inquiry by an investigating magistrate is also looking into allegations that Ms Thibout received payments from Ms Bettencourt's daughter, Ms Bettencourt-Meyers.
Defence lawyers will argue this morning that the trial cannot proceed without Ms Thibout, who sent a medical certificate last week to justify her absence.
They will also argue that the separate investigation of Ms Thibout should be completed before the trial goes ahead.
Finally, defence lawyers will challenge the accuracy of a psychiatric report which concluded that Ms Bettencourt was suffering from a form of Alzheimer's disease and was not responsible for her actions.
The lawyer will protest that the expert who examined Ms Bettencourt was a friend of the investigating judge.
The trial is taking place in Bordeaux rather than in Paris because evidence emerged in 2008-2011 that the Sarkozy administration tried to influence the original investigation.
The whole affair was put in the hands of an investigating magistrate 530km away.
Two other allegations against Mr Woerth and others for alleged illegal campaign financing and influence-peddling will be tried separately.
- Independent
