Through the late 20th century, global society experienced waves of unprecedented political and institutional change, but Australia came to be identified as "constitutionally speaking... the frozen continent", unable or unprepared to comprehensively modernise its own fundamental laws (Sawer 1967). This thesis opens up a subject basic to, but largely unexplored in debate about constitutional change: the territorial foundations of Australian constitutional thought. Our conventional conclusions about territory are first, that Australia's federal system has settled around a 'natural' and presumably final territorial structure; and second, that this is because any federal system such as possessed by Australia since 1901 is more decentralised and therefore more suitable than any 'unitary' one. With federalism coming back into vogue internationally, we have no reason to believe our present structure is not already the best. Reviewing the concepts of territory underpinning colonial and federal political thought from 1815 to the present day, this thesis presents a new territorial story revealing both these conclusions to be flawed. For most of its history, Australian political experience has been based around a richer, more complex and still evolving range of territorial ideas. Federalism is fundamental to our political values, but Australians have known more types of federalism, emerging differently in time and place, than we customarily admit. Unitary values have supplied important symbols of centralisation, but for most of our history have also sought to supply far less centralised models of political institutions than those of our current federal experience. Since the 1930s, in addition to underutilising both federal and unitary lines of imported constitutional theory, Australian politics has underestimated the extent to which our institutional treatment of territory has itself become unique. Despite its recent fall from constitutional discourse, territory is also again on the rise. While political debate has been poorly placed to see it, Australia has experienced a recent resurgence in ideas about territorial reform, offering the promise of a better understanding of the full complexity of our constitutional theory and a new 'unfreezing' of the assumption that territorially, Australia will never change. This thesis seeks to inform these vital new debates.