From their beginnings in 1917 in the Archdiocese of Mechelen in Belgium, the Auxiliaires de l’Apostolat shaped a new form of apostolate: being active as lay women in the modern world, while pursuing a life towards religious perfection. Although this new vocation was not unique, and a number of similar groups emerged at the same time, there was no institutional framework for such groups yet. Therefore, the life and position of these women was an often hard-to-understand identity in church and society, requiring them to constantly negotiate their own identity vis-à-vis institutional normative frameworks. This stalemate was in part a result of a rigid preconciliar belief that the lay faithful were excluded from a life of perfection. Besides, since they were women, there was no possibility to both take vows and at the same time live in the world – a possibility that men did have, for instance in the capacity of a priest. As such, it was partially a gendered concern. In addition, the case of the Auxiliaires de l’Apostolat offers the opportunity to reflect on other areas of tension, for instance when it comes to agency, or tensions between the local and global, as a seamless diocesan recognition did not result equally seamless in recognition by the Sacred Congregation of the Council. The present contribution develops this case in three major phases – their establishment and early development in the 1920s and 1930s, their search for canonical recognition between 1928 and the early 1960s, and the breakthrough that comes during the Second Vatican Council with the almost unpremeditated integration of their identity into the Church's self-understanding, more specifically in the conciliar constitution on the Church, Lumen Gentium 41.