At the beginning of the nineteenth century the term ‘psychology’ was almost unknown in the English-speaking world. It was described by the philosopher-poet Coleridge as an ‘insolens verbum’ (an outlandish word), but nevertheless ‘one of which our language stands in great need’. 1 Today it is commonplace. Nearly every university in the developed world provides instruction in psychology; psychologists are widely employed in many areas of public service, particularly health and education; and considerable sums of money are devoted to psychological research. At international gatherings of psychologists thousands of psychologists from sixty or more countries meet periodically to discuss a vast range of problems, both theoretical and applied. How has this rapid growth come about? Upon what foundations does it rest? What is the present state of psychology, and what are its prospects? It is to these questions that this book is addressed. It sets out to explore how modern psychology has been shaped by its history.