This book presents a critical account of the theories, hypotheses and models that have been advanced to explain and to predict population change in various kinds of societies. The author also puts forward and tests a new theoretical treatment to isolate and to explain the conditions and causes of the transition from high to low fertility rates within and among different societies. Two aspects of this new theory are the interacting effects of living standards and the constraints of time, and the economic and social factors that in turn are behind these. Among the other factors that are considered are the effects and roles of education, the availability of food, child care, the extent of the female labour force, health and infant mortality, family type, and cultural and social norms and expectations.