Environmental design was first identified by Jacobs (1961) as a factor in preventing crime or causing it. According to Newman (1973), certain design features in urban areas release latent attitudes in tenants, including a policing attitude and a territorial consciousness inimical to instructions and other criminal behaviors. Schools, public and private housing projects, and other urban environments were studied for their relationship to crime incidence. Lighting may reduce fear of crime in housing projects, but has little or no impact on school vandalism: neighboring features, however, affect vandalism, as well as child density, which increases its occurrence. Territorial behavior can be defined as a series of goal-directed, spatially dependent behaviors and cognitions which operate at various levels of social organization and foster several aspects of interpersonal functioning. Recent research developed at Westinghouse definitely links crime prevention to environmental design. Demonstration projects embodying defensible space concepts were implemented in Hartford, Conn., and in public housing developments in three cities. In the latter, despite crime, fear of crime, and residential instability, the defensible space theory generally worked. In assessing defensible space theories and research, the authors of this study find that conceptual clarification is still needed and that research is still inconclusive. Future research must address many questions, such as offenders' or potential offenders' reactions to territorial residents and cost-effectiveness of defensible space. Explanatory endnotes and 57 references are appended.