Over the last two decades, transboundary regional environmental governance has witnessed some institutional change through an increasing shift from intergovernmentally constituted political institutions to new complex structures of decision-making where policy-making has begun to adapt to a new, more active role of societal actors at multiple levels of political authority. In addressing this issue, the article raises the following questions: How can new structures and processes of public deliberation and participation in transboundary regional environmental governance be designed, and which opportunities and risks emerge? To address these questions, the article develops a normative-analytical design for regional environmental governance in ecoregions; this design defines the conditions under which public deliberation and participation conveying discourse, argument, and persuasion can help to democratize collective decision-making.