The concept of transnationalism, according to Michael Clarke, ‘is difﬁcult to place with any precision in international theory. In itself, it certainly does not constitute a theory; it is rather a term which recognizes a phenomenon or perhaps a trend in world politics’ (Clarke 1985: 146). This imprecision I take to be an advantage for the purpose of this chapter so we do not read backwards into history from the perspective of globalism as a social theory, nor do we take the internationalism of the First International as our guiding light. Instead, we simply examine transnational social movements which, in their own organization and aims, transcended national boundaries. The ﬁrst section of this chapter deals with the origins of internationalism in the European labour movement. Why did this emerge? What were its limitations? And, above all, why did the spirit of internationalism die so abruptly as the European powers lined up for the Great War? The second section takes up the story of the communist internationalists who came to the fore after 1917. What did this ‘proletarian internationalism’ actually represent in practice? Was there a less Eurocentric orientation towards the colonial revolution? The third section takes up the colonial and post-colonial situations from the perspective of transnationalism. Could nationalist movements also be internationalist? How did anti-imperialism inﬂuence the new social movements of the late 1960s? Finally, we turn to what I call the ‘contemporary cosmopolitans’. What exactly is this ‘global civil society’ they take as a foundation for cosmopolitan transnationalism? In terms of global contestation is this movement not essentially Eurocentric?