Victoria runs the most fully integrated regime under the Medical Treatment Planning and Decisions Act 2016. Your Advance Care Directive can hold both a binding instructional directive and a values directive, and you appoint a Medical Treatment Decision Maker who must decide according to what they believe you would have wanted rather than their own preference. The forms are witnessed under the Act's specific requirements, and a support person can also be appointed to help you make and communicate decisions while you still have capacity. Victorians should know that a values directive, while not binding in the strict sense, must still be given effect where possible, so it is far from decorative.
New South Wales is the outlier: there is no statutory advance care directive form, so your written wishes take effect as a common law directive recognised by the courts, while your decision maker is appointed as an enduring guardian under the Guardianship Act 1987 (NSW). The appointment must be witnessed by an eligible witness, and once you lose capacity your enduring guardian can only resign with the approval of the NSW Civil and Administrative Tribunal. Because the directive itself is common law rather than statutory, clarity and dating are doubly important, since there is no prescribed form to fall back on if the wording is ambiguous.
Queensland uses an Advance Health Directive made under the Powers of Attorney Act 1998 (Qld), and it is worth knowing that only statutory advance health directives are legally binding in Queensland, not informal common law ones. The document lets you give directions about future treatment and appoint an attorney for personal and health matters, and it carries its own execution and medical certification requirements. Queenslanders often pair the directive with an enduring power of attorney so that financial and health authority sit in a coherent package.
South Australia consolidated everything into the Advance Care Directives Act 2013 (SA): one document records your wishes and appoints a substitute decision-maker covering both medical and lifestyle matters. The witnessing standard under section 15 is stricter than for an ordinary power of attorney, because the authorised witness must certify that you understood the legal effect and appeared to have capacity. Anyone appointed as your decision-maker, or with an interest in your estate, is disqualified from acting as that witness.