Advances in urban sociology now depend on developing the temporal dimensions of ethnographic data. For public place behavior, the need is to follow people before, through, and after the sites where fly-on-the-wall researchers traditionally have observed them. To understand how people economically exploit a city's public life, researchers must follow market responses that discount and redistribute initial advantages. For explaining the formation of neighborhoods, a multiphase social theory is required. Drawing examples from Los Angeles, nine historical processes are shown to have shaped a substantively wide range of cases, including officially preserved, Orthodox Jewish, affluent totemic, low-income ethnic immigrant, and homeless service areas. A historical approach shows that the social character stamped onto a neighborhood early in its history is often effaced or reversed by later processes, identifies new formative processes, and locates the major turning point in a different period, the 1960s, than do theories stressing globalization and deindustrialization. © The Author(s), 2010.