This historically embedded treatment of theoretical debates about prerogative and reason of state spans over four centuries of constitutional development.Commencing with the English Civil War and the constitutional theories of Hobbes and the Republicans, it moves through eighteenth-century arguments over jealousy of trade and commercial reason of state to early imperial concerns and the nineteenth-century debate on the legislative empire, to martial law and twentieth-century articulations of the state at the end of empire.It concludes with reflections on the contemporary post-imperial security state.The book synthesises a wealth of theoretical and empirical literature that allows a link to be made between the development of constitutional ideas and global realpolitik.It exposes the relationship between internal and external pressures and designs in the making of the modern constitutional polity and explores the relationship between law, politics and economics in a way that remains rare in constitutional scholarship.