A French-Cameroonian writer, Charles Onana, is due to go on trial in Paris accused of complicity in contesting the 1994 Rwandan genocide.
About 800,000 Tutsis and moderate Hutus were killed within 100 days.
In a book published five years ago, Mr Onana described the idea that the Hutu government had planned a genocide in Rwanda as "one of the biggest scams" of the last century.
His lawyer, Emmanuel Pire, insists that Mr Onana does not question that genocide took place, or that Tutsis were particularly targeted.
Mr Pire told the AFP news agency that the book in question was "the work of a political scientist based on 10 years of research to understand the mechanisms of the genocide before, during and after".
Mr Onana, now 60, and his publishing director at Editions du Toucan, Damien Serieyx, were sued four years ago over the same book.
That case was brought by the NGO Survie, and the International Federation for Human Rights (FIDH) for "publicly contesting a crime against humanity".
Monday's trial is only the second case of denying the Rwandan genocide to come to trial in France.
Under French law, it is an offence to deny or "minimise" the fact of any genocide that is officially recognised by France.
Mr Onana's trial will be "historic, since there is not yet any case law strictly speaking related to Rwanda" on questions of Holocaust denial, Camille Lesaffre, campaign manager for Survie, told AFP.
"We will mainly base ourselves on case law related to the Holocaust."
In 2021, French President Emmanuel Macron asked Rwandans to forgive France for its role in the Rwandan genocide.
He said France had not heeded warnings of impending carnage and had for too long "valued silence over examination of the truth", but said his country had not been an accomplice in the killings.
Source: BBC
