This thesis explores how the development of the Post Office in Ireland was, from its inception, intertwined with and profoundly impacted by the evolution of the early modern British ‘composite state’2 in its various iterations, highlighting how Ireland’s status as a kingdom within that composite polity down to the Act of Union (1800), and thereafter as part of the United Kingdom, shaped the form and pace of development of the island’s postal service down to 1840. It traces how the post in Ireland progressed from being a small scale, ad hoc and expensive service instigated during the Tudor military campaigns of the mid-sixteenth century and dedicated to serving the needs of the ruling elite within the top echelons of the Tudor state (the monarch, Privy Council, parliament, the judiciary and senior ranking army personnel) through conveyance of official correspondence and interception of intelligence to become, by 1840, three years after Queen Victoria’s accession to the throne, an indispensable, benign yet silent pillar and servant of the state in the modern sense of the organised totality of British citizens. By tracing major developments (setbacks as well as advances) in the post in Ireland in tandem with changing ideologies concerning the state, this study explores how its accelerated growth and popularity both reflected and responded to broader modernising dynamics and trends within the increasingly broadly defined British state, and specifically in Ireland whose status within that state evolved significantly during this c.285-year period.