The history of military mobilization does not fit neatly into national boxes, not even in the modern era. The traditional military history narrative, at least as far as Europe is concerned, sees the French Revolution as an important turning point in the 'nationalization' of military service. The essays in this volume seek to challenge this view by examining largely overlooked aspects of military mobilization from the eighteenth century to the present. Whether as colonial troops, ideological volunteers, mercenaries, adventurers or soldiers who were recruited in prisoner of war camps, men and women have often found themselves fighting for a country other than their own. On numerous occasions, pressing wartime needs have compelled states to turn to transnational recruitment. At the same time, the willingness of individuals to commit to cross-border military service has endured despite the advent of nation-states; a trend that could become more prevalent in the twenty-first century.