Despite recent and growing media attention surrounding obesity in the United States, the so-called obesity epidemic remains a highly contested scientific and social fact. This article examines the contemporary obesity debate through systematic examination of the claims and claimants involved in the controversy. We argue that four primary groups—antiobesity researchers, antiobesity activists, fat acceptance researchers, and fat acceptance activists—are at the forefront of this controversy and that these groups are fundamentally engaged in framing contests over the nature and consequences of excess body weight. While members of the fat acceptance groups embrace a body diversity frame, presenting fatness as a natural and largely inevitable form of diversity, members of the antiobesity camp frame higher weights as risky behavior akin to smoking, implying that body weight is under personal control and that people have a moral and medical responsibility to manage their weight. Both groups sometimes frame obesity as an illness, which limits blame by suggesting that weight is biologically or genetically determined but simultaneously stigmatizes fat bodies as diseased. While the antiobesity camp frames obesity as an epidemic to increase public attention,fat acceptance activists argue that concern over obesity is distracting attention from a host of more important health issues for fat Americans. We examine the strategies claimants use to establish their own credibility or discredit their opponents, and explain how the fat acceptance movement has exploited structural opportunities and cultural resources created by AIDS activism and feminism to wield some influence over U.S. public health approaches. We conclude that notions of morality play a central role in the controversy over obesity, as in many medical disputes, and illustrate how medical arguments about body weight can be used to stymie rights claims and justify morality-based fears.