Community has long been considered an important form of social organization in many parts of the world. At the level of governance, communities, loosely defined, are often the targets of "outreach," "engagement," or policies aimed at "development." On an individual level, people forge identities according to places or characteristics around which they feel a "sense of community." But what happens when "community" is not just as a sense or a loosely-bounded social construct, but a formal legal entity? This research investigates a participatory slum upgrading policy that operates by forming just such entities. The Baan Mankong ("Secure Housing") program of Thailand provides urban residents at risk of eviction with access to home loans and legal land tenure, but only as communities. To take part in the program, residents must be part of an official chumchon ("community"). Residents are often aided in forming and registering their chumchon by two very different organizations: (1) the government-sponsored agency that administers the policy, and (2) an activist network made up of other chumchon, which facilitates the arduous process of organizing households to go through the many stages of Baan Mankong upgrading. Once formed, the chumchon is the unit through which households collectively negotiate with landowners, take out loans for physical upgrading, and gain rights to occupy land collectively. Through Baan Mankong, thousands of urban households have become bound to chumchon financially, spatially, socially, and politically. My proposed dissertation project looks into the origins and effects of these chumchon in terms of (1) the ideologies that underlie them, (2) the organizational principles at work within them, and (3) the individuals that comprise them.