This thesis has three objectives. Its primary objective is to examine, and critically evaluate, the theoretical accounts offered by Hans Kelsen and Joseph Raz to explain the temporal continuity and discontinuity of legal systems. In particular, it evaluates the explanatory power of those accounts by combining an abstract analysis of the accounts in principle and an evaluation based on systematically applying them to one concrete, historically circumstanced instance: the legal systems of British derivation in Australia between 1788 and 2001. The thesis thus tests each account’s factual fit: how adequately it corresponds to, accords with, and persuasively makes sense of, the facts – including complex social facts, attitudes and normative standards – for which it purports to offer an account. Second, the thesis aims to demonstrate, more generally, the utility of applying theoretical accounts to a particular historical instance to complement abstract analysis. Third, the thesis aims to advance the understanding of the evolution of Australian legal systems between 1788 and 2001. These three objectives are achieved through the critical exposition and reconstruction of the accounts, their development and enrichment where refinement is appropriate, their application to the specific context of Australia and their evaluation, individually and in comparison.