This working paper calculates measures of the level of socioeconomic segregation in large metropolitan areas (cities and their surrounding suburbs) in the United States and France. The authors define “large” metropolitan areas as city-suburb combinations with a population of greater than one million. They use tract data from the American Community Survey (2006-2010) and data from the French Census of 2008 and the French Ministry of Finance. The results reveal a significantly higher level of socioeconomic segregation in large American than in French cities. American cities are more segregated than French cities on all three measures considered here: income, employment, and education. This finding holds with measures that account for different distributions of income, unemployment, and education across the two countries. The researchers also find (1) a strong pattern of low-income neighborhoods in central cities, and high-income neighborhoods in suburbs in the United States, but not in France; (2) that high-income persons are the most segregated group in both countries; (3) that the shares of neighborhood income differences that can be explained by neighborhood race-ethnic composition are similar in France and the United States, suggesting that racial segregation cannot account for much of the higher level of U.S. socioeconomic segregation.