Reflecting on the contrary experiences of Timor-Leste and Bougainville, an autonomous region of Papua New Guinea (PNG), this chapter considers the role that constitution making can play in building new states. It begins by outlining the role that constitution making can play in state-building. It then synthesizes the literature on deliberation, discursive participation and public participation in constitution making to demonstrate the importance of public participation in constitution-making and addresses skepticism about its role. To provide context for the empirical comparison it then outlines the background to constitution-making and state-building in Timor-Leste and Bougainville, and analyses the role that public participation in constitution making has played in state-building in the two cases. Based on this comparison, this chapter concludes by arguing that constitution making can play a positive role in state-building, although this will depend upon the level of public participation involved. Participation can be measured along a continuum. At one extreme, participation is minimal and the constitution is made by local elites or imposed by an external force, or there are opportunities for participation but the outcomes have little impact on the resulting constitution. In these circumstances, the Timor-Leste case illustrates that this is unlikely to play a positive role. At the other extreme, there is extensive public participation, in which there is widespread public consultation and genuine opportunities for their feedback to shape the future constitution. The Bougainville case suggests that this is likely to play a positive role. Therefore, the higher the level of public participation in constitution making, the more likely it will play a positive role in state-building, by fostering a sense of political community and by producing a constitution that enhances the legitimacy and effectiveness of state institutions.