Thierry Meyssan () is a French conspiracy theorist, journalist, and left-wing political activist.
He is the author of investigations into the extreme right-wing, particularly France's National Front militias, as well as into the Catholic church.
Meyssan's book ' (L'Effroyable imposture) challenges the official account of events of the September 11 terrorist attacks.
Meyssan is president of the Voltaire Network, which had been a respected independent think tank prior to the publication of 9/11: The Big Lie. His reputation helped raise his conspiracy theory to prominence.
Meyssan has been noted as using cross-citations of other conspiracy theorists' works in order to lend the appearance of credibility to his ideas. Regarding the events of 9/11, Meyssan cited Webster Tarpley; Tarpley cited David Ray Griffin; and Griffin cited Meyssan.
In 2002, he published a book on the September 11 terrorist attacks, with the English translation titled 9/11: The Big Lie. Meyssan argued that the attacks were organized by a faction of the US militaryâÂÂindustrial complex in order to impose a non-democratic regime in the United States and to extend US imperialism. It is one of "the first wave of book-length conspiracy speculations" in France and Germany about 9/11.
A follow-up to his first book titled LâÂÂeffroyable Imposture II (The Big Lie 2) accused Israel of carrying out the assassination of Rafic Hariri.
French media quickly dismissed the contents of the book, and a Pentagon spokesperson also deprecated the book.
In 2005, the U.S. State Department declared Meyssan a persona non grata due to his active promotion of misinformation about the United States.