This thesis explores the internal workings of the Earls Fitzwilliam core estates in Yorkshire and Ireland from 1815 to 1865. While the Yorkshire estate benefitted from the presence of a resident landlord, the family’s Irish holding in county Wicklow enjoyed a far greater degree of autonomy devolving power to a resident land agent. This comparative study aims to examine the different management strategies introduced in each location and how decisions made impacted local communities. The configuration of the estate administration structure in each location varied considerably due to the different environments in which they operated. While the Irish estate was primarily agricultural in nature, its Yorkshire counterpart contained sizeable mineral reserves which necessitated a more complex management structure. Consequently, these differences resulted in very different power dynamics in each location. Furthermore, outside the management structure resided the tenantry of various gradations who relied on the estate for their livelihoods. Through the analysis of estate records, church records, parliamentary papers, print media and census material, this study charts the trajectory of two aristocratic landed communities located on opposite sides of the Irish Sea from the early to mid-nineteenth century. Case studies are utilised throughout to demonstrate the complex connections and difficulties that existed in each location. It exposes how the estate administration sometimes clashed over decisions concerning the management of the estates, and how decisions made ultimately affected landlord, agents and tenants as all were intrinsically connected by a shared reality.