The Great War, as it was known until 1939, set in chain a series of catastrophes and crises that have largely defined the long twentieth century: economic, political, cultural, and metaphysical. Philosophy was not unaffected, either within academe, or more widely. Nearly each of the major philosophical movements, from analytic philosophy through to post-structuralism, was directly or indirectly formed in response to the civilizational crisis the Great War inaugurated, and different perceptions of its causes and significance. This chapter surveys the territory, and looks forwards to the different contributions collected here.