In the religious history of Lreland, the pilgrimages to Lough Derg and Our Lady's Island have occupied a special place of interest for centuries. The pilgrimage practice at Lough Derg offers insights into certain aspects of study which warrant further attention in pilgrimage scholarship. Historians have generally overlooked the significant shifts in the nature of the pilgrimage exercises brought about as a result of the Counter-Reformation. Efforts to transform the pilgrimage from a ritualistic experience into an inner spiritual experience demand a proper investigation into the nature of these devotional shifts. Ln the early seventeenth century pilgrims at Lough Derg performed ritual actions sanctioned by custom and transmitted by oral tradition. However, in the early eighteenth century the religious event was reshaped by the Franciscans. Pilgrims were provided with written instructions and encouraged to meditate on their actions, turning the ritual into an example of Tridentine spirituality. This study attempts to compare the significant shifts in the nature of the Lough Derg pilgrimage with other Irish pilgrimage sites such as Our Lady's Island, Croagh Patrick and Struell Wells. It is also the objective of this study to investigate the antiquity of traditional practices modified by the clergy. Traditional practices were subject to minute shifts over time. The main aim in this thesis is to examine how newly invented traditions became accepted and embedded, and how they were in turn, expanded on.