The economic and physical decline of urban neighborhoods has become a widespread and widely misunderstood phenomenon in post-war America. It has not been restricted to aging central cities: most growing cities and many suburbs possess areas of decay as well. After decades of changing occupancy, dwellings have fallen into disrepair, and the quality of public facilities and services has also declined. But a scattering of neighborhoods, only recently regarded as hopelessly decayed, have experienced visible regeneration, often without material government assistance. Because these patterns of decline and rebirth are poorly understood, they raise important questions for analysis and policy. This essay examines the meaning and causes of neighborhood succession, and the relationship between succession and decline. The essay is divided into the following parts: (1) The Determinants of Spatial Separation of Income Groups; (2) Residential Neighborhoods and Submarkets: Some General Concepts; (3) The Concept of Neighborhood Succession; (4) A Framework for Analyzing Neighborhood Succession; (5) Processes and Causes of Neighborhood Succession; (6) The Causes of Neighborhood Physical Decline; (7) Neighborhood Abandonment; (8) Formulating Neighborhood Stabilization and Revitalization Strategies. Four figures are included. (BJV)