Andrew Stewart and George Williams, leading scholars and media commentators, explain what has been called the most important decision of the Australian High Court since the Tasmanian Dam Case in 1983. They show what was being argued and why it was being argued, as well as what was decided and the implications for Australia’s future. They include key passages of the majority judgment, and from the dissents of Justices Kirby and Callinan. Is this “a destabilising intrusion of direct federal lawmaking into areas of legislation which, since federation, have been the subjects of State laws” (Justice Kirby)? Might it reduce State Parliaments to “impotent debating societies” (Justice Callinan)?