Public health ethics has emerged and grown as an independent discipline over the last decade. It involves using ethical theory and empirical analyses to determine and justify the right thing to do in public health. In this paper, we distinguish public health ethics from clinical ethics, research ethics, public health law and politics. We then discuss issues in public health ethics including: how to weigh up the benefits, harms and costs of intervening; how to ensure that public health interventions produce fair outcomes; the potential for public health to undermine or promote the rights of citizens; and the significance of being transparent and inclusive in public health interventions. We conclude that the explicit and systematic consideration of ethical issues will, and should, become central to every public health worker's daily practice.