"Theories of rational addiction posit that certain habit-forming goods-characterized by an increasing marginal utility of consumption-generate predictable dynamic patterns of consumer behavior. It has been suggested that attendance at sporting events represents an example of such a good, as evidenced by the pricing strategies of commercial sports interests. In this essay, we provide new evidence in support of rational addiction for the case of Major League Baseball but fail to find such support in data from the Korean Professional Baseball League. We then review the scientific literature on sports fans from the perspective of human behavioral ecology and propose a theory of endogenous habit formation among sports fans that could explain our findings". ("JEL" C32, D83, D87, D91, L83) Copyright 2007 Western Economic Association International.