Using data from the 1991 and 2001 Censuses, I examine patterns of ethnic diversity and segregation in England’s metropolitan regions. Diversity is measured using the Shannon entropy index and segregation is measured using the Theil index. Both indices can be decomposed into contributions due to region, district, and ward, which may indicate the processes responsible for patterns of ethnic diversity and segregation. The results show that ethnic diversity increased from 0.533 in 1991 to 0.731 in 2001. Between 1991 and 2001 the share of diversity contributed by Inner London and the West Midlands declined and the share contributed by Outer London and the Outer Metropolitan Area rose. Decomposition of total diversity shows that regional and district differences in ethnic diversity increased between 1991 and 2001 but differences between wards declined in importance. Within-ward diversity contributed more than 75% of total diversity at each census. Between 1991 and 2001 there was a slight increase in the overall level of segregation. Decomposition of total segregation into between-district and within-district components for each region shows that the contribution of within-district segregation to total segregation fell between 1991 and 2001. However, the contribution of between-district segregation to total segregation remained important and increased significantly in Inner London. Across the area investigated wards have on average become more ethnically diverse but there remain significant differences in diversity and segregation between regions and districts.