The aim of this thesis is to investigate the relationship between political authority and economic change in the tenth to twelfth centuries AD. This is often interpreted as a period of dramatic economic and political upheaval; enormous growth in commerce, the emergence of an urban network and increasingly centralised polities are all indicative of this process. Ireland has rarely been considered in discussion of this sort but analysis of Ireland’s political economy has much to contribute to the debate. This will be tackled through a consideration of the coinage struck in Ireland between c.995 and 1170 with focus upon the two themes of production and usage. In analysing this material the scale and scope of a monetary economy, the importance of commerce and the controlling aspects of royal authority will each be addressed. The approach deployed is also overtly comparative with material from other contemporary areas, particularly England and Norway, used to provide context. Ultimately, in seeking to analyse these questions within this comparative context, the issue of where economic agency behind changes in the European economy will be considered. Chapters 1 and 2 situate the research within the wider scholarly debate and precise historical context respectively. Chapters 3 to 6 are a consideration of the manner in which the Hiberno-Scandinavian coinage was produced and administered. This reassesses questions of the scale of production, administration and the role of royal authority in the production of the coinage based upon a comprehensive re-categorisation and re-dating of the material. Chapters 7 and 8 concern the use of coins in the urban environment of Dublin and across the entirety of Ireland, with coinage analysed within its archaeological contexts. Ultimately, this thesis suggests that monetary economy and levels of commerce were substantial, variable and yet relatively geographically constrained. When considered in relationship to contemporary political contexts, the importance of royal authority in directing the economy is determined to be minimal with agency behind economic change seen to rest with an urban, mercantile community.