This thesis is contained in two volumes comprising text and plates. The chapters in volume one deal in turn with the composition of the heraldic executive, the duties undertaken by the Officers, the heraldic records kept by them, and the painters who were attached to the Office of Arms. The chapter is divided into three time-periods and for each a detailed account of the duties of the Lyon King of Arms is given, along with the activities of certain Officers. The existing Armorial Manuscripts for each of the three periods are also considered, along with a summation of the knowledge that Officers possessed of the science of heraldry during the late sixteenth and early seventeenth century. An appendix gives biographical details of all known Officers of Arms from the period 1567 to 1625. The second volume consists of Plates showing examples of heraldic art in the many forms created during the reign. The Plates are grouped to correspond to each chapter subject in volume one.