Although Marguerite Yourcenar (1903-1987) lived in the US for almost fifty years and became an American citizen in 1947, few people understand the influence her experiences in the United States had on her work. Biographers, critics and scholars have wrongly imagined she was untouched by her life in America – that she remained French to the core, linguistically isolated, culturally «pure», that she never took an interest in the country where she lived for half her life. Drawing on Yourcenar’s fiction and non-fiction works as well as on her voluminous archives at Harvard’s Houghton Library, this innovative analysis sheds new light on Yourcenar’s American inspirations and influences. A previously unreleased interview of Marguerite Yourcenar by the American journalist T. D. Allman, a letter from Marguerite Yourcenar written in English, an amazing photograph from Life magazine, and entries from her companion Grace Frick’s diaries are among the documents, mostly previously unpublished, which bring to life the American side of Yourcenar’s literature. This study also reveals that Marguerite Yourcenar, far from being limited to French, had an outstanding mastery of the English language. It shows how, thanks to her understanding of America and its language, she became an authentic heir to a long and vivid American tradition: protest literature.