Originally published in 1925, according to the preface, Instinct: A Study in Social Psychology is the result of many years of interrupted labors that began in a graduate seminar in 1909–1910, when the author attempted to apply Professor McDougall’s classification of instincts to the classification of criminals. The immediate result was the conviction that McDougall’s instincts were habits, and further constructive work found issue in an unpublished report on “Instinct and the Social Sciences,” taking issue with McDougall’s viewpoint regarding the significance of the theory of instincts then prevalent for the social sciences. Finally completed after many years in the making, this work is the result of the author’s investigations on the topic of instinct. Today it can be read in its historical context. This book is a re-issue originally published in 1925. The language used and views portrayed are a reflection of its era and no offence is meant by the Publishers to any reader by this re-publication.