The public sphere is a pivotal concept in democratic theory. Conventionally, it is framed in a local/national context. In the classic Habermasian formulation, the public sphere is predicated on national media, a sovereign state, and participatory citizenry. However, under conditions of globalisation, the nation-state paradigm is subject to increasingly significant challenges. The advent of the network society is also destabilising the institutional foundations of the national public. These developments necessitate a reassessment of the public sphere as a territorially delimited realm. A reconstruction of Habermasian theory reveals how global interconnections may be providing the structural preconditions for the emergence of transnational public spheres. The categories of flows are threefold: communicative networks, governance networks, and activist networks. In certain issue-areas, all three preconditions may coalesce to produce an environment suitable for the emergence of transnational public spheres. However, the potential for the realisation of ‘borderless’ public spheres is circumscribed by key factors. Global communication is systematically distorted, global governance is democratically deficient, and the norms of critical publicity are difficult to sustain amongst highly differentiated virtual audiences. Unless these issues are addressed, the early promise of transnational networks as an emancipatory force will be neutralised.