Governments often act in the name of security to protect their citizenries. For example by legislation or by the recruitment and employment of large numbers of armed personnel to detect and prosecute violent crime, or via engagements in military interventions to repel or pre-empt foreign attacks. These practices are often taken to have strong moral justifications. The value of security is linked to the value of life and the disvalue of violence and injury, and all of these are central both to theoretical accounts of and common sense views about the difference between right and wrong. The essays in this volume seek to increase our understanding of state action in the name of security and take a range of viewpoints and approaches. Some articles attempt to delimit the concept of security, or dispute attempted delimitations; some consider security as a 'good' and ask what sort of good it is, and how valuable; whilst others consider the relation between state action in the name of security and state action in the name of other goods, notably liberty, or consider ethical issues in health security, climate security and cybersecurity. Overall, this collection of essays shows how appeals by governments to the value of security have grown out of relatively recent events and processes at a global level, such as the response to pandemics, the acceleration of climate change, and counter-terrorism. The volume features an introductory essay and forms part of a five-volume series on legal ethics and the enforcement of law.