Despite the extensive scholarship on the eleventh and twelfth century ecclesiastical reform movement, the roles that lay noblewomen played within the reform have often been overlooked. This thesis focuses on the correspondence between lay noblewomen across Europe and clerical reformers, chronicle excerpts, and several vitae of women from this period in order to study laywomen's participation in all aspects of the reform movement. An analysis of these sources points to the emergence of a new perception of lay female religiosity, one built upon the belief in a politically and socially active female agent of the Christian Church who could use her position in her family and her rank as a member of the nobility to influence and support the efforts of the reform movement. This thesis contributes to the growing scholarship focusing on the role of gender in medieval religious history, and suggests that the importance of women within the reform dynamic was greater and more complex than hitherto suspected.