The decline of human fertility that occurred in Europe and North America in the nineteenth century, and elsewhere in the twentieth century, remains a topic of debate largely because there is no accepted explanation for the event. Disagreement persists in part because researchers have rarely used the detailed quantitative information necessary to form adequate tests of alternative theories. This paper uses district-level data from Bavaria to study the correlates of the decline of fertility in that German kingdom in the nineteenth century. Bavaria's fertility transition was later and less dramatic than in other parts of Germany. The European Fertility Project, the most influential study of the European fertility transition, used very large units of analysis and unrefined measures of economic and social conditions. This project concluded that the fertility transition reflected the simultaneous adoption of new ideas about contraception, and was not caused by adaptation to changing economic and social circumstances. We use smaller units of analysis, better measures of the possible determinants of fertility, and more appropriate econometric methods to study Bavaria's fertility transition. Our results indicate that the European Fertility Project was right about the role of religion and secularization, but missed an important role for the economic and structural effects stressed by economic historians.