Public health is about taking collective action to protect and promote the health of populations. For example, vaccination and screening programmes help avoid or ameliorate diseases; health education and promotion help make people healthier. Public health is underpinned by research, including epidemiology. Public health research is enormously beneficial but also creates ethical issues. Some are familiar from standard research ethics, but with a public health 'twist'. For example, what sort of informed consent is required when research involves large data sets used by epidemiologists? Other issues are distinctive to public health research: should ethical restrictions on research be lifted during public health emergencies, for example? This book analyses current ethical issues in public health research. Rigorous discussions are informed by insights from standard research ethics, from philosophy and bioethics, and from the author's related research and experience as Chair of Public Health England's Research Governance Review Group. An overarching theme of the book is the trade-off between one's right to decide to participate in public health research versus the communal duty to do so.