Accounts of the concepts of function and dysfunction have not adequately explained what factors determine the line between low-normal function and dysfunction. I call the challenge of doing so the line-drawing problem. Previous approaches emphasize facts involving the action of natural selection (Wakefield 1992a(Wakefield , 1999a(Wakefield , 1999b or the statistical distribution of levels of functioning in the current population (Boorse 1977(Boorse , 1997. I point out limitations of these two approaches and present a solution to the line-drawing problem that builds on the second one.A Case. Mr. Smith is a 70-year-old man being admitted to the hospital with congestive heart failure (CHF). He had a heart attack a few years ago, followed by a procedure that reopened a blocked coronary artery. He did well since then, and tests showed that his "ejection fraction," the amount of blood his heart pushes out in each contraction, remained around 50%, down from the average of 60% but still in the normal range.Over the last few weeks, he has developed increasing shortness of breath, and tests show that his ejection fraction has dropped to 20%. This reduction in his heart's pumping ability is causing fluid to leak out of the veins in his lungs, causing his trouble breathing. Possible causes of his heart failure range from another heart attack to valvular problems or other issues. *Received January 2005; revised May 2007. †To contact the author, please write to: Indiana University Center for Bioethics, 410 W. 10th Street, Suite 3100, Indianapolis, IN 46202; e-mail: phschwar@iupui.edu. ‡Thanks to Christopher Boorse, Randall Dipert, Gary Ebbs, Gary Hatfield, Harold Kincaid, Eric Meslin, Shari Rudavsky, and Alfred Tauber for conversation and encouragement regarding my work on these issues. Thanks to two anonymous reviewers for Philosophy of Science for critique and questions that significantly contributed to the final product. Thanks also to audiences at