Recent archival research in France and the United States has cast new light on the extraordinary role played by the American Hospital of Paris during the First World War. Major advances in medicine took place inside the Hospital, thanks to the outstanding volunteer doctors and surgeons from scores of American medical schools who worked there. The American government's policy of neutrality in the period 1914-1917, essentially ruled out financial aid directed at military activity. As the aid provided by the American Hospital was humanitarian in nature, the Hospital quickly emerged as the epicenter of a wholly unprecedented effusion of American volunteers–doctors, nurses, ambulance drivers, as well as massive flows of philanthropic donations to finance their humanitarian work. And for many Americans this entire effort was a way to demonstrate opposition to the neutrality policy of President Wilson until 1917.