Francis Ysidro Edgeworth (1845-1926), scion of a leading Anglo-Irish family, was a classical scholar and mathematician who became the Drummond Professor of Political Economy at Oxford. He was the leading mathematical economist of his day and made major contributions to utilitarian ethics, probability theory, and statistics. Though little understood at that time, Edgeworth's work on contract theory has increasingly been recognized as vital to recent advances in game theory and the optimizing properties of markets under varying conditions. As editor of the Economic Journal, as a major contributor to Palgrave's Dictionary of Political Economy, and as an inveterate reviewer of books on all subjects and in five European languages, Edgeworth's range of expertise was extraordinary by modern standards. Three volumes of Papers Relating to Political Economy were published during Edgeworth's lifetime. This volume completes the project by including three important monographs -- Mathematical Psychics, New and Old Methods in Ethics, and On the Relation of Political Economy to War -- alongside all the articles and reviews that were not included in the first three volumes. In addition to a selection of Edgeworth's contributions to the Palgrave Dictionary, this volume also contains a complete bibliography of Edgeworth's writings compiled by Alberto Baccini. It is prefaced by assessments of Edgeworth's life and works written by the editor, Peter Newman, the leading authority on the subject.