The coastal areas of the Ganges-Brahmaputra-Meghna delta are acknowledged hotspots of environmental and social concerns. This reflects a large, mainly rural population of 56.7 million, which is exposed to a range of natural hazards exacerbated by climate change, sea-level rise and subsidence. There are high levels of poverty and limited social well-being, including poor access to education, health, drinking water, and sanitation facilities. A spatial assessment of social vulnerability can indicate which communities are more susceptible to environmental hazards, while a temporal assessment may indicate how such vulnerability is changing due to development and other drivers. This study provides the first analysis of social vulnerability across the entire coastal delta within Bangladesh and India. It uses consistent and common secondary data at the sub-district level for two time periods: 2001 and 2011. These are used to construct a socio-economic vulnerability index across the region using Principal Component Analysis. Three main conclusions emerge. Firstly, there is a cross-shore social vulnerability gradient across the whole delta, with more vulnerable people living near the coast. Here, the benefits of access to marine fisheries are not apparent. Secondly, non-agricultural development and economic expansion have reduced the vulnerability significantly, showing its benefits. Lastly, despite general positive development trends, shocks due to major cyclone landfall appear to have enhanced vulnerability in the impacted areas. Further comprehensive analysis across the whole delta is recommended to improve our understanding of the common threats and possible solutions.