Categories of the ‘Art of the Impossible’: Achieving Sustainable Uniformity in Harmonised Legislation in the Australian Federation

National uniform legislation links the federal distribution of powers achieved more than 119 years ago with the challenges and opportunities faced by Australia in an interconnected world. Over this span of time, developing national uniform legislation has been described as the ‘art of the impossible’. The main objective of this article is to critically examine the database of national uniform legislation with a view to applying public policy and federalist theory to explain how sustainable uniformity has been achieved. Rather than focusing on why an individual set of uniform Acts has not achieved a high level of uniformity or has diverged through unilateral amendment, this article examines national uniform legislation by analysing the factors at play. This approach allows the common patterns impacting sustainable uniformity to be identified. From among 84 sets of uniform Acts, four discernible links with theory have been found: (1) the ‘incrementalism and policy cycle’ model—to explain harmonisation that may take decades (31 sets); (2) the ‘multiple streams’ framework, explaining legislation that emerges as sustainably uniform from the outset due to an ‘open policy window’ (16 sets); (3) ‘pragmatic federalism’ solutions, such as skeletal legislation and the conferral of powers, which are developed in the course of inter-jurisdictional negotiations when uniformity is required but is particularly difficult to achieve (14 sets); and (4) the ‘advocacy coalition’ framework, which in contrast, explains situations where jurisdictions hold firm views about retaining diversity (23 sets). Developing and drafting national uniform legislation can become the ‘art of the possible’ with this improved understanding.