Gentlemen Prefer Blondes: The Intimate Diary of a Professional Lady (1925) is a comic novel written by American author Anita Loos. The story follows the dalliances of a young blonde gold-digger named Lorelei Lee "in the bathtub-gin era of American history." Published the same year as F. Scott Fitzgerald's The Great Gatsby and Carl Van Vechten's Firecrackers, the work is one of several famous 1925 American novels which focus upon the insouciant hedonism of the Jazz Age.

Originally serialized as a series of short sketches in Harper's Bazaar magazine during the spring and summer of 1925, Loos' sketches were republished in book form by Boni & Liveright in November 1925. Although dismissed by literary critics as "too light in texture to be very enduring," the book garnered the praise of many writers including F. Scott Fitzgerald, James Joyce, William Faulkner, and H. G. Wells. Edith Wharton hailed Loos' satirical work as "the great American novel" as the character of Lorelei Lee embodied the avarice and self-indulgence that characterized 1920s America during the presidencies of Warren G. Harding and Calvin Coolidge.

Loos' lighthearted book became the second-best selling title of 1926 in the United States and a runaway international bestseller. It was printed throughout the world in over thirteen different languages, including Russian and Chinese. By the time Loos died of a heart attack in 1981 at the age of 93, the work had been printed in over 85 editions and adapted into a 1926 comic strip, a 1926 silent comedy, a 1949 Broadway musical, and a 1953 film adaptation of the latter musical.

Loos wrote a sequel, But Gentlemen Marry Brunettes, in 1927. Decades later, Loos was asked during a television interview whether she intended to write a third book. She facetiously replied that the title and theme of a third book would be Gentlemen Prefer Gentlemen. This quip resulted in the interview's termination.