Queen Elizabeth II holds the distinction, unique in the world, of being head of state (or Sovereign) in more than one nation. The nations over which she reigns, the Commonwealth Realms, are all components of the now-dismantled British Empire. Over the course of the twentieth century, each realm increasingly expressed its independence and individuality. This independence has been developed and demonstrated within the framework of a shared head of state. Though each realm is legally independent and in no way subordinate to any other, this framework adds a degree of complexity to their political and cultural structures which deserves more attention than it has received in the past. This thesis employs institutional theory to examine the ramifications of sharing a head of state. What consequences arise from this sharing arrangement? How are the benefits or costs distributed? To whom do these accrue? Can they be distributed through different methods? How and why has the system remained relatively stable over the past 60 years? The head of state the realms share, and the structure which has evolved to make this possible, is a pronounced commonality. The realms‟ reactions to this commonality, however, are quite diverse. The role of the monarch varies from realm to realm, as does the role of her representative. Each country has nationalised their sovereign to a greater or lesser extent. Some have incorporated the monarchy into not just their laws, but also their culture. Others have sought to minimise their association with the monarchy. Upon close inspection, it appears that the differences between the Commonwealth Realms are not in their relationship with the broad structure (the crown) they share, but in many smaller details. While such details may appear insignificant, their impact on the shared structure is important. Their principal effect upon the structure is in their capacity to create and influence the perception of that structure. The significance of such perceptions should not be underestimated. Perceptions of the shared structure clearly recreate that structure in a continuous feedback loop; a cycle of perception, modification, and operation. This feedback loop is probably the most significant ramification of sharing a head of state to be found within the shared structure as it exists at present. The loop has the capacity both to reinforce the structure‟s strengths, and to further its limitations. Thus, it is a major factor in the system‟s potential perpetuation or collapse. However, the shared structure, as it presently exists, is a complex and organic structure which is constantly evolving. Its flexibility allows for adaption to new circumstances; circumstances which might even include changing perceptions of the structure itself. This resilience serves to dampen the negative effects of the loop. It does not eliminate the perpetuation of the structure‟s potential weaknesses, but it may help reduce their impact. This would indicate that the feedback loop is rather weak; its effects are somewhat muted. This thesis is a study of constitutions, their operation, and the perceptions of them. By analysing institutions it develops the hypothesis that such constructs do not exist within a vacuum, and that the perception of them is a powerful factor in their establishment and perpetual recreation. The supposition that a feedback loop may help to explain the ongoing evolution of institutions is an original contribution. Furthermore, through an analysis of the Commonwealth Realms, and their shared Head of State, this thesis specifically considers a subject which is not frequently studied. Indeed, these nations have never been systematically examined as a collective group. In addition to these contributions, the method of study utilised herein is unique in this field. This is not a legal study, a political study, or a sociology study. Rather, it takes a multidisciplinary approach to the material. By considering this subject from the perspective of numerous fields, a unique understanding of the topic emerges. This holistic approach is one of the most effectively ways of considering the subject, and is, in itself, a contribution to scholarly understanding.