David Ricardo's “On Machinery” chapter continues to interest theorists and historians of economic thought (Blaug 1958, Hollander 1979, Kurz 1984, Samuelson, 1988, 1989, Morishima 1989, Negishi 1990). Yet the addition of the chapter to the third edition of Ricardo's Principles of Political Economy and Taxation arguably overturns much of the view for which Ricardo is so well known (Davis 1989). In the added chapter Ricardo allows, contrary to his original view in the first two editions, that the introduction of machinery is indeed injurious to the class of laborers. More interestingly, because machinery substitutes for labor, wages cannot rise and profits are no longer threatened by rising rents. Effectively the contest between capitalists and landlords of the first two editions of the Principles is replaced in the final edition by one between capitalists and laborers. However, not only does the “On Machinery“ chapter substantially change the distributional argument customarily attributed to the Principles, but it also permits an examination of Ricardo's thinking about distribution in two distinct, but related frameworks. The discussion here compares the distributional analysis in the first two editions with that of the third to explain the general nature of the Ricardo's theory of profit. It does so by providing a novel interpretation of Ricardo's characterization of profit as a residual, and by emphasizing the historical context in which distribution occurred in the beginning of the nineteenth century.