This book is a companion volume to the Royal Economic Society edition of The Works and Correspondence of David Ricardo, edited by Piero Sraffa with the collaboration of Maurice Dobb. It completes the record on Ricardian value theory by showing Ricardo's reaction to Malthus's pamphlet The Measure of Value Stated and Illustrated of 1823. Ricardo's Notes are, in Sraffa's words, 'the only considerable item' not appearing in the Royal Economic Society edition of his works. In addition, the recent publication by Cambridge of the variorum edition of Malthus's Principles of Political Economy, edited by J. M. Pullen, makes it possible to understand Malthus's pamphlet as an intermediate step between the 1820 and 1836 editions of the Principles. In his introduction Pier Luigi Porta highlights the place of these Notes in the development of Ricardo's thinking. When taken with Ricardo's paper on 'Absolute Value and Exchangeable Value', these Notes provide the essentials of Ricardian value theory.