The subject of this book is the nature of under-developed economies and their behaviour over the long term. A study of economic evolution cannot ignore structural factors since the two are partly interdependent, for just as such factors are essential to the explanation of economic circumstances so changes in these circumstances will modify the structural factors themselves. I have discussed structural issues more specifically in my study Revolution industrielle et sous-developpement, 1 and the research I undertook then made me aware that there is a notable gap in the large and often distinguished literature on the Third World -- the lack of comparative studies of its economic development. While there are several case studies on the development of individual countries, or small groups of countries, and also some studies of broader scope dealing with certain aspects of this development, there are none (as far as I know) which might help to single out the various characteristics of economic development in the Third World over a long enough period (i.e. the last seventy years) or for a large enough number of countries to make the analysis applicable to all the less-developed countries, or at any rate all the larger ones.