This chapter explores post-war socialist internationalism as an experiment in international relations – one meant to offer a distinct and even alternative form of international relations to the better-known one dominated by state actors. The purpose of the socialist internationalism was never simply instrumentalist in a directly political sense. By the end of the nineteenth century, institutionalised cooperation between socialists across party and national lines had become a fundamental characteristic of socialism, contributing to the creation of an international socialist community. And as a community, socialist internationalism functioned as a site for socialists to consult on issues of common concern and to work out ’socialist’ positions on them. If this endeavour affirmed and reaffirmed the collective commitment to the community, it also actualised the hope of identifying policy positions distinct from those of non-socialists and especially of non-socialist governments.