PROJECT SUMMARY/ABSTRACT This is a study of neighborhood change and its impacts on trends in Black-white segregation over a multi-decade time span. It will provide much new information about settlement patterns that continue to impact residents’ health, social class mobility, and quality of daily life. It will trace changes in population composition at the neighborhood scale within constant geographic boundaries and evaluate how different patterns of neighborhood change contributed to increasing or declining segregation in the larger urban area. It will compare the period 1930-1950, 1950-1980, and after 1980. An important contribution of this project is to develop a neighborhood-scale data base with consistent boundaries over time for multiple decades to support the proposed analyses. It will use methods developed for the Longitudinal Tract Data Base (LTDB) for 1970-2020 and the Urban Transition HGIS Project (1880-1940). A major effort will be to incorporate data and map sources that are now becoming available. The project will develop harmonized neighborhood data for 69 major cities for 1930-1950 and for them plus their surrounding suburbs for 1950-2020, making possible detailed studies of suburban development after World War II.