This article examines the changing meaning of property in Bombay over the twentieth century. It suggests that the Ownership Flat, with ownership rather than tenancy in apartment buildings, was a novel form of property that emerged in the city over the course of the century. The Ownership Flat has become the hegemonic form of dwelling in Mumbai and is the desired outcome of far-reaching urban renewal interventions. Yet while the idea of ‘ownership’ implies an unproblematic relationship between ‘owner’ and ‘property,’ this article suggests that the Ownership Flat represented a major shift in the idea of urban property. In particular, while the Ownership Flat was a cuboid in the air enclosed by walls, ceiling and floor, real property as understood by the law meant land and immoveable property upon land. Further, ‘ownership’ of flats in Bombay was exercised through the cooperative housing society, a peculiar legal institution where the society as collective owned the building containing Ownership Flats. A conceptual gap emerged between the popular practice of buying and selling ownership flats and the legal framework within which such transactions took place. By excavating the contingent rise of ownership and by examining the unresolved challenges posed to the idea of property by the Ownership Flat, this article offers a new perspective on the emergence of the propertied subject in urban India.