Urbanization is a fundamental driver of a changing world in this 21st Century. In 1997, the National Science Foundation established two urban sites as part of its long term ecological research program: the Baltimore Ecosystem Study (BES) and Central Arizona-Phoenix (CAP) projects. These two sites were distinct not only because they focused on novel ecosystems, cities, but also because they were expected to examine cities as dynamic, social-ecological systems over the long term. Over the past 20 years, BES and CAP have played a significant role in the development of and interest in social-ecological research in general and urban ecology in particular. This session will examine the historic role of BES and CAP to the fields of urban ecology and ecology as social-ecological phenomena; synthesize research from four key domains—streams and watersheds, biodiversity, residential lands, and long term social-ecological dynamics; and consider the future role for long term, social-ecological research for the field urban ecology. An important component of the symposium will be to consider what it will take for urban ecology to transition from a “frontier science” to a “textbook science.”