This chapter analyses the development of transnational policing as a crucial element of the federal–transnational security regime of the German Confederation, which the Congress of Vienna had established in 1815 to maintain external and internal security. Narratives of cross-border political subversion and crime triggered new modes of political and transnational policing in nineteenth-century Europe, resulting in both formal police cooperation as well as in various actors and techniques of transnational policing and securitisation. Through the ‘commission-mode’ and the ‘conference-mode’, policing agencies aimed at intelligence, surveillance and suppression, and contributed to the production and dissemination of a systematic knowledge base on political subversion and international crime. In the process, they influenced the development of security narratives and logics and practices of securitisation, and constituted important elements of the emerging European security culture.