This book examines the theme of internationalism, in the form of opposition to nationalism, racism and war, in the context of French history, and in particular of the French socialist and working-class movement. Beginning with the defence of Dreyfus against anti-Semitism, it covers antimilitarism before 1914, opposition to the First World War, the advent of Communism, then the rise of Stalinism, fraternisation with German soldiers during the Nazi occupation, and support for national independence in Indochina and Algeria. It looks at individuals and political organisations, many of them neglected by mainstream history, who argued against nationalism and took practical action in defence of internationalist principles.