The ease, speed and sophistication with which extremist groups have exploited cyberspace for operational coordination and ideological proselytising have taken Western governments by surprise. From brazen digital advocacy of extreme and violent ideology to deft recruitment and fundraising, the Internet has proven to be a remarkably useful medium for non-state actors and hostile terrain for states seeking to curtail the growing global influence of violent extremism. This chapter charts the trajectories of policy frameworks of one distinct cluster of states confronting similar challenges in this respect: the “Anglosphere” states of Australia, Canada, New Zealand, the United Kingdom and the United States of America. The apparent challenge for these Anglosphere states is that policy officials recognise that transnational counter-terrorism challenges cannot be resolved unilaterally but require collaboration in two crucial dimensions. First, to achieve meaningful sovereignty over cyberspaces requires government to acquire the cooperation of private sector actors – including large multi-national digital technology firms. For these companies, relinquishing commercial data or giving up encryption to authorities is anathema. Second, as extremist operational and proselytising activities can transfer across jurisdictions effectively instantly, states have sought to build multi-jurisdictional coalitions, pooling expertise, intelligence and, most importantly, resources. This chapter articulates how these imperatives have played out in domestic institutional settings and goes on to describe how Anglosphere states have forged robust though low-profile networks of security collaboration that facilitate policy and operational interchange. The Anglosphere transgovernmental alliance, it is contended, operates as a persistent and influential mode of policy-making for all partners, cognitively framing the “problem” of extremism in cyberspace and underpinning significant technical and strategic collaboration.