Prerna Singh has written How Solidarity Works for Welfare: Subnationalism and Social Development in India (Cambridge University Press, 2015). Singh is the Mahatma Gandhi Assistant Professor of Political Science and International Studies at Brown University and faculty fellow at the Watson Institute. How do sub-units of government meet the everyday needs of their residents? Do they vary in how well they provide basic health and education services? Singhs book makes a novel argument about these questions with extensive original data collection. How Solidarity Works suggests that sub-national units, states and provinces, can develop solidarity between residents. When this solidarity is high it is associated with developing strong regimes of social welfare programs. Conversely, when sub-national solidarity is low, there is little basis around which to provide for those in greatest need. This intricately argued book marshals an enormous amount of original information about several states in India. The empirical findings and larger theoretical argument are remarkable and worthy of replication outside of India.