Vilfredo Pareto is a key figure in the history of economics and sociology. His sociological works, which attempted to merge these two disciplines, hinge upon a psychologistic analysis of society, economy and politics. Much has already been written on Pareto but this is the first book to rethink his contribution to classical sociology by focusing upon its psychological underpinning.The author locates the origins of Pareto's psychologistic approach to sociology, both within the history of Italian thought, and within Pareto's own experiences of business and politics. He then evaluates Pareto's sociology through the lens of contemporary social science, to reach the conclusion that its explanatory power may well be growing rather than diminishing, as levels of social and epistemological complexity rise. The author also looks at Pareto's assumptions concerning human personality through the lens of contemporary psychology, showing that Pareto's sociology is likely to be of particular value to those interested in political psychology. The book concludes with a psychometric study of Westminster MPs which clarifies and attests to Pareto's contemporary relevance, leaving readers with the thought that practitioners of politics may also gain much by reading Pareto.