It has long been recognised that ‘the political and organisational making of the German proletariat was begun abroad by a minority of proletarianised journeymen artisans’.1 From the mid-1840s on, the centre of this development shifted from Switzerland and France to London. Here, in the quintessential metropolis-London was twice the size of Paris, and three times larger than Vienna or New York-the German artisans were exposed to entirely new working and living conditions. The main developments in German socialism and the ‘making’ of the socialist movement took place here. It was also in London that the Communist Manifesto was commissioned. One organisation, in turn, dominated the politics of early German socialism in exile, the Communistischer Arbeiter-Bildungsverein (CABV). Founded in 1840, and active until nearly the end of the First World War, the CABV not only became an important focal point of Vormärz radicalism, but was also home to many leading socialists fleeing reaction after the defeat of the 1848-1849 revolution. Correspondingly it became to an equal extent the site of their own efforts to unite among themselves, to define their own distinctive position and programme, and to settle upon the best form of socialism in an era of many socialisms and widespread disagreements about strategy and aims. This chapter considers the origins of the CABV and its relation to continental organisations such as the League of the Just and the Communist League, and traces its changing attitudes to alternative concepts of socialism, especially those of Marx and Engels. It also argues that the London émigrés’ attempts to develop theories and organisational forms of internationalism, underestimated in recent accounts, were in fact vital to their distinctive brand of socialism. Finally, the impact of the emigrants returning to Germany in 1848-1849 is analysed.