These problem areas typically have 200 or more dwellings and are clearly insulated from their environment by material and symbolic boundaries. They are usually poorly maintained and often have very young residents and a high concentration of single-parent families. The work conducted by the National Association for the Care and Resettlement of Offenders has focused on involving residents in planning improvements so that they will be motivated to maintain and protect them. The Department of the Environment launched an initiative in 1979 to improve housing management and reduce the number of vacant properties in projects that are difficult to rent. The Land Use Research Unit at King's College has changed the design to increase surveillance and defensible space, based on the concepts of Jacobs and Newman. The three projects appear to have reduced crime. Various explanations have been offered for these results, based on factual data. However, subjective explanations based on recognition of the importance of residents' involvement may be more accurate. 54 references.