Part I examines the nature and development of the Crown, and this chapter analyses key moments in the transition from feudalist royal autocracy to constitutional monarchy in England, focussing on Crown prerogative and reserve powers. Parliament's increased role in the Tudor constitution in the sixteenth century was the precursor to further dramatic constitutional changes throughout the seventeenth-century Stuart era. By the end of that century, royal absolutism had been replaced by the emergence of a constitutional order with parliamentary supremacy the cornerstone. Myths and legal fictions played a role in the incremental evolution of Westminster parliamentary democracies and an indivisible Crown. In the twentieth century a Commonwealth of Nations emerged. Now we have multiple versions of the Queen’s ‘two bodies'. Each of the realms over which Elizabeth II reigns as sovereign is a distinct body politic. Some of those polities have federal structures, and the states or provinces are additional separate and discrete Queen’s bodies within one realm. New Zealand retains perhaps the most ‘pure’ form of Westminster parliamentary sovereignty and parliamentary sovereignty anywhere in the world.