Transnational regulation involves profound changes in the ways rules are set today. Based on two case studies on Internet governance and the regulation of corporate financial reporting, we show that transnational governance is best understood as a dynamic, non-linear process. In both fields, regulatory institutions are constantly renegotiated between public and private actors, a process which gives rise to new, hybrid, forms of authority. The hybridization of authority challenges the common distinction between public and private authority in transnational regulation. We propose to characterize the ongoing dynamics as transnational governance spirals. Our comparative analysis follows a research strategy of causal reconstruction. To that end, we identify three mechanisms serving as analytical tools to explain transnational institution building and the observed governance spirals: integration, authorization and formalization.