The Assault on Truth: Freud's Suppression of the Seduction Theory is a book by the former psychoanalyst Jeffrey Moussaieff Masson, in which the author argues that Sigmund Freud, the founder of psychoanalysis, deliberately suppressed his early hypothesis, known as the seduction theory, that hysteria is caused by sexual abuse during infancy, because he refused to believe that children are the victims of sexual violence and abuse within their own families. Masson reached this conclusion while he had access to several of Freud's unpublished letters as projects director of the Sigmund Freud Archives. The Assault on Truth was first published in 1984 by Farrar, Straus and Giroux; several revised editions have since been published.

Jeffrey Moussaieff Masson is an American author. Masson is best known for his conclusions about Sigmund Freud and psychoanalysis. In his The Assault on Truth (1984), Masson argues that Freud may have abandoned his seduction theory because he feared that granting the truth of his female patients' claims would hinder the acceptance of his psychoanalytic methods. Masson is a veganism advocate and has written about animal rights.