Foster specializes in the history of modern France and the French Empire. Presently she offer courses on Modern France, the French Revolution, France and Africa, France in the Second World War, Europe in the Twentieth Century, the First World War, and a global survey entitled Empires and Nations. Her first book, Faith in Empire, explores French colonial rule in West Africa through the prism of religion. Based on archival research in France, Senegal, and Italy, it examines the relationships between French Catholic missionaries, French colonial administrators, and Muslim, Christian, and animist Africans in colonial Senegal between 1880 and 1940. Students in her France and Africa course have the opportunity to refute her findings by working with translations of archival documents created by French administrators, African officials, and French missionaries in 1890s Senegal.