Established in 1919, the Hoover Institution Library & Archives at Stanford University is perhaps the world's largest repository of materials related to war, revolution, and peace movements across the globe, with especially rich collections related to the First World War. This article explains the origin and mission of the library, which was created by Herbert and Lou Henry Hoover following their World War I–era work in humanitarian aid, food relief, and diplomacy. Outlining significant holdings related to the war—including not just official records but rare ephemera such as posters, lace, and propaganda—this article explains the Hoovers’ vision of building a vast and varied repository of material that would establish the library as a hub of research on war and revolution. By acquiring significant historical material, the founders and curators sought to encourage future generations of scholars to theorize and employ solutions for building peace worldwide. The article also discusses the library's holdings related to Stanford students who served as ambulance drivers, pilots, soldiers, and nurses during the war—collections that provide valuable insight into the lived experience of the war and document Stanford's contributions to interventionist/anti-interventionist discussions before America's entry into the war in 1917 and, later, to the Allied war effort.