“Wildland-Urban Interface” (WUI) areas are the focus of current fire policies in the United States. Hundreds of Community Wildfire Protection Plans (CWPPs), as mandated by the Healthy Forest Restoration Act of 2003, have begun to delineate WUI boundaries on the ground, prioritizing WUI areas for hazardous fuels reduction treatments—essentially turning a social-political construct into a physical reality, with potentially major ecological consequences. This study includes a comparative analysis of WUI delineations, based on existing legislation, as they have been applied through CWPPs in the southwest; I also address some of the associated challenges posed for ecologists and land-managers. Preliminary estimates for Arizona's 2-million acre western Mogollon Plateau region indicate a high degree of variability, with WUI areas encompassing 8% to over 25% of the landscape, depending on the decision criteria applied. Using a GIS-based approach, I demonstrate the ecological significance of the WUI delineation process and the potential impacts on songbird diversity, Mexican Spotted Owl and Northern Goshawk habitat, and other wildlife species in northern Arizona. Ultimately, WUI areas offer a unique opportunity to integrate biodiversity conservation, restoration and urban ecology, and fire hazard reduction; they can be merely an extension of our urban footprint, or alternatively a redefinition of our relationship with the surrounding landscape.