Biography of X is a 2023 alternative history novel by American writer Catherine Lacey published by Farrar, Straus and Giroux.

[1] The book includes fictional citations and end notes; Lacey, for the most part, devised these as she wrote the novel rather than after she was finished.

[7] Dwight Garner, in a positive review in The New York Times, compared Lacey's writing to that of Renata Adler and Janet Malcolm.

[9] In a review published by The Los Angeles Times, Jessica Ferri praised Lacey as "one of the most fearless novelists writing today".

[13] In March 2024, The Atlantic included Biography of X in its list of "Great American Novels" that have been published in the past century.