Peace is generally defined as a state of non-belligerency between states. This means that it is defined negatively as the absence of war. So is peace just a pause between two wars? In French, the term is significant: peace is considered a slice of life between two conflicts. Thus, we speak of the early 20th century as the «Belle Époque» and we talk about the «interwar period», which implies the failure of peace. Twenty years after the end of the Great War, another, even more terrible conflict began. At the same time, an inversion of values took place in European minds that along with the horrors of war made it very difficult for any Franco-German reconciliation to take place. We would have to wait for the end of the Second World War and its consequences to speak of peace as a realistic utopia. This volume brings together a number of articles in Portuguese, French and English – on topics such as «thinking peace», intellectuals and peace, federalism and universalism, religiosity and secularism, women and peace, and campaigns and mobility – from many prestigious experts and young researchers. They bring new ways of thinking and interdisciplinary perspectives, and provide an attentive, critical reading of the core subject. This volume proposes to substantiate concepts, projects, movements, speeches, images and representations, and to deepen the knowledge of the key personalities who thought about peace between 1849 and 1939.