This article examines the role of the United States in the long French debate over separating church and state. From the visit of Alexis de Tocqueville to the 1905 law, key constituencies studied closely the American experience, debated its merits, and argued over its applicability to France. What emerged was a complex pattern of engagement. Depending on their particular domestic imperatives, French observers saw an American system that enshrined religious liberty, fostered atheism, or allowed the Catholic Church to become a threat to republican liberties. The influence of the United States reached a peak in the crucial years of 1903-5, when the American experience directly inspired a key clause in the 1905 law, and all sides used America to defend or attack the proposed legislation. Recognizing this brings a much-needed international dimension to the scholarship on the 1905 law and the separation of church and state.