Historians of economic thought have failed to notice the contribution of Simon Nelson Patten to the development of the concept of consumer's surplus. Patten, a professor of economics at the University of Pennsylvania from 1888 to 1917, a founder and president of the American Economic Association, was a recognized leader of the nascent economics profession in the United States;1 but he has been all but forgotten by contemporary economists. This Note attempts to correct that historical oversight by recognizing Professor Patten's ideas on the concept of consumer's surplus. Patten disputed briefly with Marshall over the meaning and measurement of consumer's surplus and may have induced Marshall to make a minor alteration in his statement of the concept in the third (1895) and subsequent editions of the Principles. Unlike the founders of marginal utility theory (Jevons, Menger, and Walras) and unlike Marshall, Patten considered the utility of a good to a consumer to be a function of the quantities of all goods he consumed. In his Theory of Dynamic Economics (1892) Patten treated extensively the cases of complementary and substitute consumer goods. In this analysis he should be credited with some originality, since he seems to have developed on his own the concepts of complementary and substitute consumer goods from the discussion by the Austrian economists, particularly Wieser, of complementary factors of production. These concepts were not new when Patten wrote his Dynamic Economics, but, as far as can be determined, he was unaware of any prior discovery. For example, he apparently was unaware of the mathematical formulation of a generalized utility function by Edgeworth in 1881 and of the discussion of consumer's surplus, which