This dissertation explores struggles over citizenship and the practice of politics in communities situated along the railway tracks in the growing Northeastern Thai city of Khon Kaen. I develop the concept of "citizen design" to explain how contemporary disagreements along the tracks over land rights and new urban planning projects reflect contestations over notions of good citizenship. Such politics, I argue, resonate with broader transformations in Thailand's social order. In Thailand, "citizen design" is not a new practice. Rather, successive eras of state and non-state development initiatives have been imagined as means of transforming the nation's "villagers" into proper citizens. Throughout this history, technologies of administration, democracy, security, authenticity, and sufficiency have reproduced a developmental notion of citizenship that marks the poor as needing training prior to deeming them capable of "ruling and being ruled." Through an ethnographic examination of the Thai state's new participatory housing policy, the Baan Mankong (Secure Housing) project, I show how this logic persists and is being challenged. Although envisioned as a means of stabilizing the social order, transforming the city, reforming the values of the poor, and producing harmonious urban communities, Baan Mankong has become a site of these politics in its own right. This research, conducted between 2008 and 2010, follows government architects, NGO activists, and residents of the railway communities, exploring the intersection between the project's aims of "developing people" (patthana khon) and the residents' efforts to secure lease rights to their land. I show how poor communities use the policy to make claims to being legitimate citizens, while development experts attempt to reform participants' values through the policy's trainings, community organizations, and spatial designs. Instead of creating united communities as the policy's discursive framework suggests, the planning processes intensified disagreements over distributions of power among local activist networks, rights to the city, and visions of citizenship. These disagreements reveal how those living on the cusp of belonging in both city and nation are reclaiming politics to reconfigure normative notions of citizenship, transforming Thailand's political order in the process.