This book attempts to present a detailed and critical account of the thought of Antoine-Louis-Claude Destutt de Tracy (1754-1836). Major importance has been placed on the analysis of his published writings. Biographical details have been provided only to the extent necessary to elucidate the circumstances of the composition and publication of his writings: in particular, the intellectual and political currents in France during the Revolutionary and Napoleonic periods. The book has three main themes. The first is Tracy's philosophy of ideologie, which was concerned to clarify concepts and provide guarantees of reliable knowledge. The second is Tracy's attempt to elaborate a science of social organisation, la science sociale, whose objective was to recommend institutions and policies which could maximise social happiness. The third theme is Tracy's development of liberal and utilitarian approaches to the fields of politics, economics and education. This study began life as a doctoral dissertation at the London School of Economics and Political Science. I am grateful for the guidance of my supervisor, Professor Ken Minogue, and for helpful comments from Professor Maurice Cranston, Professor Jack Lively, and Dr John Hooper.