The Atlantic Ocean not only connected the Americas with Europe through trade routes, but also provided the basis for a stead exchange of knowledge and ideas, including political radicalism. Socialist and anarchists would use this ‘radical ocean’ to escape state prosecution in their home countries, and establish radical milieus abroad. However, this was often a rather unorganised development and therefore the ties that existed were quite diverse. The movement of individuals led to the establishment of organisational ties, the import and exchange of political publications between Europe and the Americas, as well as vice versa. To show the transatlantic networks of political radicalism evolved, with regard to socialist and anarchist milieus in particular, is the main aim of the present book and it therefore looks at actors within the relevant processes, that have so far been not of interest for the major histories of transnational political radicalism in the lat 19th and early 20th centuries. Individual case studies will consequently be merged with a broader context to show how networks were actually created, functioning, and impacting the history of the radical Atlantic.