Professor Le Roy Ladurie is the leading exponent of the `new' history of the French school. His achievement has set an example to historians in all other countries. As the diverse studies in this volume show, he has particularly revolutionised the study of population change, offering new techniques and posing new questions. In mapping new territory he insists upon measurement together with insight into social and psychological issues. These he studies in his unique style. He urges that demography is a fundamental determinant of economic change. He calls this the source of `the immense, slow-moving fluctuations' and the huge cycles of rising and falling pressures on supply. `History that is not quantitative cannot claim to be scientific,' says Ladurie.