Investor-state dispute settlement (ISDS) first emerged in public and parliamentary debates in the lead-up to Australia signing its free trade agreement with the United States in 2004, and the official reason for excluding ISDS was mutual trust in each other’s domestic legal systems. However, a few civil society groups had raised broader sovereignty concerns. Debates intensified from 2010, when Australia joined with the United States (and 10 other Asia-Pacific economies) to negotiate the expanded Trans-Pacific Partnership. ISDS continues to be hotly debated, but there has still been almost no sustained analysis of how Australia’s domestic law protections for (all) investors compare to substantive protections for foreign investors under international customary and treaty law.