Urban residents have been using internet technologies for civic and political discussion since the earliest days of Usenet. A large part of this online talk is distinguished by its informality and spontaneity. This dissertation analyzes informal discussion as actually practiced in everyday, computer-mediated settings. The project considers the ways in which online discourse operates at a moment in political life in which day-to-day issues of urban living are articulated, contested, and brought into focus as public concerns. Using data collected from a 1.5 year online ethnography based in Philadelphia, Pennsylvania, the dissertation characterizes this informal, publicly-oriented discussion as networked public talk. Networked public talk has four principal characteristics: (1) the primary activity is sustained discussion among citizens; (2) it is talk characterized by informality, not governed by procedural rules or a pre-existing agenda; (3) it is mediated through networked technologies and comprised of publicly-viewable discussions; and (4) it involves issues of collective concerns, rather than purely personal issues. What constitutes these public matters is not pre-determined nor are the issues predefined—they emerge and take shape through public talk. The concept of networked public talk foregrounds the relationship between informal political discussion and a specific moment in public life in which participants are sifting through, articulating, and bringing into focus what are their collective concerns. In this sense, networked public talk is conceived as political because it is through talk that citizens demonstrate that an issue should be a matter of common concern. The dissertation proposes that informal talk online be understood as a process of making sense of public issues. It looks at three components of that process in online urban forums: the ways in which public issues are brought to attention, articulated, and sustained as focal points of conversation through the use of internet technologies as discussion mediums; how an information architecture and established participant norms both support and constrain a sometimes serendipitous encounter with a multiplicity of perspectives; and how the networked discussion and recognition of public issues is mediated through and helps to construct lived material places.