This landmark treatise of 1817 formulated the guiding principles behind the market economy. Author David Ricardo, with Adam Smith, founded the "classical" system of political economy, a school of thought that dominated economic policies throughout the nineteenth century and figured prominently in the theories of John Stuart Mill and Karl Marx. A friend and colleague of James Mill, Thomas Malthus, and Jeremy Bentham -- each of whom exercised a decided influence on his intellectual development -- Ricardo elevated economic theory to hitherto unprecedented levels of sophistication. His clear and consistent definition of the classical system included the foundation of the tenets of diminishing returns and economic rent, which led to the doctrines known today as distribution theory and international trade theory, or comparative advantage. The Ricardian system continues to influence and inform modern economic thought, and The Principles of Political Economy and Taxation is essential reading for students of the social sciences.