Why should you read a book on economic growth? Because the subject is important: it is about the well-being of our societies today and in the future; and because it is beautiful. It carries wonderful ideas, some exposed more than 2000 years ago, spanning all civilizations. You will certainly marvel at Ibn Khaldun's prescience, at Mo Tzu's wisdom, at Solow's depiction of transition phases, at Dorfman's incredible intuition in solving variational problems.

This book is not quite the same as other books. Economic growth has attracted, particularly in the last hundred years, countless, excellent writers who have developed the field into an immense array of topics, from theoretical to empirical. Rather than trying to cover all developments – of which you can have an idea through the bibliography – I have wanted to tell you what I found fascinating in the subject. But my hope is also that you will find here a useful introduction to this wide area of research, because a lot of the book is not only on ideas but on methodology as well.

A further reason for me to write this text was to submit personal views and present new results. For too many years I have expounded growth theory by dividing the subject, as many did, into two main strands of thought: positive, or descriptive theory on the one hand, normative on the other. I am now convinced that those two strands should be unified – hence the title of the book. For clarity's sake, I think however that both approaches to the theory should be first presented separately (parts I and II), and then unified (part III).