This thesis aims to show that the Columban Society made definable and significant contributions to the Australian Catholic missionary movement. The scope of the thesis is an analysis of the work of the Missionary Society of St Columban (Columban Society) in Australia from 1920-2000. Rather than the Society’s foundation in Ireland or its overseas missionary work, the focus is the activity of the Columban Society in Australia. The thesis argues that the Columban Society helped advance the understanding and practice of overseas mission within the Australian Catholic Church in four major ways. Firstly, by organising support for its own missionary venture in China and elsewhere, it helped foster mission mindedness among Australian Catholics and established structures for the ongoing resourcing of missionary activity. Secondly, it set up seminaries to train missionary priests and later opened its reformed tertiary level missionary formation programs to all church personnel in Australia. Thirdly, it helped mould Catholic opinion through its commentary on such international issues as Australian relations with Asian peoples. Finally, it contributed to the development and dissemination of new Catholic theological teaching, particularly in relation to social justice and indigenous churches, religious dialogue and the connections between faith and ecology. The Columban Society carved out a position for itself in Australia through negotiating with the local Catholic Church. Starting as a group of diocesan priests and, from 1920 onwards, tapping into the numerous Irish church personnel in Australia, the Society grew to become a missionary arm of the local church. It created a network of financial support and influence at the grass roots level in parishes and schools through a system of regular visits, collections and a monthly magazine. As the world and church changed, it added mission education programs that fed back to Australian Catholics ideas and experiences coming from the new indigenous churches. The distinctive contribution of the Columban Society to the Australian Catholic Missionary Movement lies in its close relationship with diocesan based parish Catholics and the teaching role it developed about missionary experiences of overseas churches within the context of international affairs. The Society has a significant placewithin the social history of Australia because of the direct influence it had on the opinions of the more than a quarter of the Australian population who identified as Catholics. The history of the Society is also a case study in the application of the reforms of the Second Ecumenical Vatican Council of the Catholic Church 1962-1965 and the consequent redefinition of orthodox belief and practice.