Ethics, or bioethics, has several definitions. These include how we ought to live or practice medicine, a branch of moral philosophy dealing with right and wrong, codes of practice or practical decision support in modern health care. It exists at the interface of medical practice and the society we live in and seems to vary between countries with differing moral norms and laws, although many think that there should be or indeed are universal moral norms. Many people’s ethics emerges from their upbringing in a single culture and tradition, guided by parents, family, community and faith. Attempts to construct more human rather than divine norms have led to several moral theories, which this chapter will explain. The areas in ICU where ethical issues are important will then be reviewed: making decisions to limit treatment, including admission to ICU and stopping or limiting life-sustaining therapies in ICU; consent for treatment; how to manage disagreements, including second opinions; ethics support to the healthcare team and families and moral injury prevention.