The increased visibility of concentrated urban poverty has posed a variety of intellectual and policy challenges in the past decade. The spread of joblessness and economic disinvestment has left many urban neighborhoods in ruins. Fears about the culture and family life of the poor have motivated a variety of responses, including the recent “welfare reform” effort that ended the federal government’s guarantee of financial assistance to dependent children. The author has argued in previous papers that the underclass thesis--which draws a sharp distinction between the underclass and the mainstream--has served an ideological role with respect to social changes in two spheres: work and family. In this paper, Stern extends the argument to another sphere of social life: the public sphere. The underclass thesis is explicit in its predictions of what we should expect to find with respect to public participation. That is, underclass neighborhoods should be characterized by low levels of public participation, few social institutions, and profound neglect of public places. Moreover, we should find a discontinuity between levels in areas of concentrated poverty and the rest of the city. This paper examines public participation and the underclass from an empirical perspective. Stern uses three SIAP data sources to examine the role of arts and cultural institutions in the social life of Philadelphia. The first is a survey of public participation, conducted in five Philadelphia neighborhoods during the summer and fall of 1997, which examines the relationship of participation in neighborhood institutions, cultural participation, and evaluations of quality-of-life. The second is an assessment of physical traces of attention and neglect in these five neighborhoods and one additional community. The third is a compilation of social and community institutions for the entire Philadelphia region. These data sources provide three distinct perspectives on the concept of participation--the individual structure of participation, the physical residue of public engagement and disengagement, and the institutional structure of participation.