A substitute decision-maker (SDM) is a person who is chosen to make health care decisions for you should a severe illness or injury prevent you from making these decisions for yourself. The document that grants this decision-making power to the person selected is called a representation agreement, proxy directive, or another name depending on the province or territory.

An SDM may also be called a health care representative, agent, or proxy.

Although laws vary by province or territory, a substitute decision-maker can usually make treatment decisions (if health professionals agree with these decisions) at the end of life or anytime a person is not able to communicate. As soon as you select an SDM, it is important to thoroughly discuss and document health care preferences, such as when to continue or abandon life-support measures.