This chapter is about the ethical implications of health sector actions intended to change individuals' or communities' weight. We consider these implications using two hypothetical cases. The first is Megan, a 15-year-old girl whose BMI is in the range defined as obese. She has been unable to lose weight and her parents are considering seeking clinical help. The second case is the population of the state where Megan lives, in which 35% of adults and 15% of children are reportedly overweight, and 17% of adults and 5% of children obese. The minister for health, prompted by these statistics, is determined to take action. What ethical issues are relevant for Megan, her parents, and the health professionals they may consult? What ethical issues are relevant for the citizens of the state, their minister for health and their bureaucrats? How does a focus on the care of individuals impact on public health, and how might community-level interventions affect people like Megan? Interventions designed to treat and prevent obesity in individuals and in communities raise important ethical issues. These issues are both distinct and overlapping; because the interventions have different goals, risks and benefits, moral compromise is always necessary. The central task is to think through the ethical and philosophical issues before action is taken: whether in clinical medicine or in public health. We present ethical approaches that can assist in such reasoning.