This special issue focuses on transnational governance, essentially cross-border networked forms of co-ordination in which non-state, or private, actors play important or leading roles in providing standards, rules and practices that other actors voluntarily abide by. While not denying the pre-eminent role of the state in governance, we nonetheless believe there is an under-estimation of transnational governance in Southeast Asia and the varied governance role played by non-state actors that go beyond that of simply acting as pressure or advisory groups lobbying or advising states and regional organisations. We provide five different case studies that explore in detail the varied governance roles played by non-state actors using the common analytical framework set out in this introduction. The case studies reveal interesting variations in the architecture of transnational governance, why they emerge, the modes of social co-ordination through which they work to shape actor behaviour and achieve impact, their normative implications, and how these governance schemes intersect with the state and national regulatory frameworks. This special issue, thus, highlights the variegated architecture of governance in this region in which non-state actors play substantial governance roles regulating the conduct of other actors.