This chapter describes patterns and trends in urban decline in the United States, emphasizing changes that have taken place at the census tract level over the past four decades. Urban decline is often perceived to be synonymous with urban shrinkage. The chapter focuses on two concepts that are related to decline: distress and disadvantage. These two terms appear rather frequently in urban scholarship, where they are typically given operational definitions to facilitate quantitative analysis. By linking the two concepts with decline, the chapter presents a replicable strategy for detecting decline in empirical investigations. Concentrated disadvantage (CD) exists when multiple layers of disadvantage intersect in a single location. Several authors have proposed strategies for quantifying CD in the United States with indicators from Census Bureau datasets. With that limitation in mind, social science researchers generally concede that CD is measured for geographically-based populations.