Thomas Roberts Malthus is typically considered a ‘classical’ economist together with Adam Smith and David Ricardo. However, in important respects his view differed fundamentally from theirs, as Keynes emphasised in his biographical essay on Malthus. Most importantly, Malthus vehemently opposed Ricardo’s doctrine that it was impossible for effective aggregate demand to be deficient. Keynes, who also insisted on the possibility of effective demand failures, therefore considered Malthus to have been a precursor of his own view. The chapter discusses the following themes. What was the classical conception of ‘Say’s law’ and what were the reasons why Ricardo endorsed and Malthus rejected it? What were the main lines of reasoning in the ‘general glut’ controversy between Malthus and Ricardo? Was Keynes justified in considering Malthus’s doctrine to foreshadow his own doctrine, and if not, why not? What are the reasons why according to Pasinetti the classical (Ricardo-Sraffa) approach to the theory of relative prices and income distribution is compatible with Keynes’s principle of effective demand?