This essay discusses different approaches to studying transnational activism in historical perspective. In doing so, it concludes a review dossier in which several historians have commented on aspects of Daniel Laqua's book Activism across Borders since 1870: Causes, Campaigns and Conflicts in and beyond Europe (London, 2023). The author responds to the preceding pieces by addressing the contributors’ questions and arguments, while also noting how their pieces have applied his book's framework to different causes (e.g. anarchism, feminism, human rights, humanitarianism, labour). Moreover, this essay raises several wider points regarding the subject under consideration. For example, it stresses that activists’ notions regarding the interconnectedness of different causes could generate fresh ruptures. The discussion highlights the amorphous nature of transnational activism, including its potential use by vastly different movements, and it situates the book within a broader, and developing, research agenda.