Most historians like to open their discussion of the French economy with a flourish of statistics. Their desire to measure the performance of the economy is entirely laudable. But a word of warning: eighteenth and nineteenth century statistical sources are notoriously unreliable! Mayors in rural communes, for example, had a reputation for compiling official statistics with a scant regard for accuracy. It is hardly surprising that historians have occasionally arrived at widely divergent appreciations of particular economic variables, notably the growth of agricultural production in the eighteenth century, or levels of industrial productivity in the nineteenth. This should not be taken as a counsel of despair. One of the great strengths of many recent studies has been the application of economic theory to historical data from France. Quantitative historians have displayed considerable ingenuity in overcoming the drawbacks to their sources, using tithe registers, for example, to estimate agricultural production, or information on raw materials to calculate the output of an industry. They have also agreed international standards for drawing up national accounts, which permit some confidence in comparisons made between France and her major rivals. Nonetheless, students of the subject would be well advised to grit their teeth and look closely at the ‘sources and methods’ sections of the various studies, in order to familiarize themselves with the nature of the exercises involved. They should also be aware that for all the precision arrived at by historians, historical statistics cannot aspire to the accuracy expected of their late twentieth century counterparts.