Abstract: Until now, little has been understood about the German economy in the 1500s. The majority opinion in the current literature includes important inaccuracies, including that (1) this economy and the population continued to grow until the onset of the Thirty Years War in 1618; (2) peasant rents were flat; and (3) serfdom receded in importance. This has resulted in misinterpretations of the social history of the period as well. The core of this study draws upon the very rich records of the Holy Ghost Foundation (also known as the Poor Needy Foundation) in the town of Memmingen, in south Germany. These records detail the tithes, rents, taxes, and debt paid by the local peasant population and the forms of social control over these toilers used by the foundation. The picture painted by these records has been filled out with comparisons with other regions of Germany and feudal Europe and contrasted with developments in the Netherlands and England. The medieval economy in Germany went through two long cycles 500–1650. At the end of the first cycle, European civilization collapsed in 1348 into widespread warfare and plague. Germany then experienced an economic recovery from about 1400 to 1450. But the feudal lords, through military victories in the 1380s, 1450, and 1525, consolidated their power over the peasants and cities, so the German economy—rural and urban—stagnated from 1450 to around 1550, after which it slid into a decline that accelerated after 1600, then collapsed into the Thirty Years War. Throughout the period 1450–1618 rents, taxes, and debt imposed on the peasants rose inexorably, and forms of social control—including serfdom—grew more strict and widespread. The population of Germany also was stagnating at least by 1560 and declining by 1600. Germany did not advance into capitalism—or into the 'early modern state'—in the 1500s (as England and the Netherlands did) because of these victories of the feudal nobility. The roots of the Thirty Years War are to be found in this social, political, and economic stagnation, not religious differences.