The relation between demographic phenomena and economic development is a complex one and has changed throughout time; today the relationship is still unclear and the effects of population growth on development and social welfare are still a matter of debate. In this book, Claudia Sunna examines how this relationship has been considered in the history of economic thought, from Mercantilism to the beginning of the 20th century, demonstrating how it has been a common feature in Mercantilist, Classical, Marginalist, Neoclassical, and, Keynesian paradigms. Sunna argues that the ideas of marginalist authors on population and development in particular mainly went beyond the analytical frame of economic theory due to the fact that in the static model that they developed, population was an exogenous variable. Sunna considers such economists as Wicksell and Pareto with their theory of the 'optimum population', or Marshall with his theory of long period growth who tried to consider the population variable in the new analytical frame. Others, like Jevons, Walras, Edgeworth, Sidgwick, dealt with this subject in non-analytical works. Sunna argues that all were influenced by the classical scheme and that even Keynes, up to the end of the Twenties, used a classical way of reasoning in order to explain unemployment as a demographic phenomenon. This book will be of interest to student and researchers in history of population theory and economics development, as well as those adopting an interdisciplinary approach to demography and sociology.