This work is a reflection about and case study in Apostolicity. It is also about the power of an individual to be a change agent in socio-political contexts. Its subject is Dr. Michael Cassidy who is founder and former international team leader of African Enterprise, an international Evangelistic organisation, that partner with churches in Africa to foster the growth of the Christian movement in cities through its ten national indigenous teams spread through Africa. Cassidy is also regarded as a prominent Evangelical leader at home and abroad, and is a strong influence in the Lausanne movement. The thesis traces the ministry of Cassidy in his years leading up to the founding of the work and his nearly 50 years of witness in the turbulence of Africa and South Africa during and after the Apartheid years. This historical review has special interest for the ecumenical witness of the church in its fight against Apartheid through great conferences like The Durban Congress on Mission and Evangelism 1973, The South African Christian Leadership Assembly (SACLA l and SACLA ll), the National Initiative for Reconciliation and the Rustenburg Church Consultation. In the research the theological, missiological and philosophical motifs of Cassidy’s work are discussed, with special attention to the issues of truth and the socio-political implications of love. The thesis also describes Cassidy’s involvement in the Marriage Alliance and the struggle to bring a biblically based outcome to the South African legislation on the matter of gay marriage. Cassidy’s worldview and his spirituality, weighed against the current debate on these issues, are examined. A primary interest expressed in the thesis is the concept of Lay Apostolicity, a concept that was powerfully raised by Cassidy whose ministry has been as a layman who has not been ordained. The structures for mission are deeply examined from Protestant and Catholic perspectives. The writer argues that Cassidy’s ministry has special value as a model and example for others in understanding and participating in the apostolic ministry of the ordinary Christian man and woman in the local church or in the working context. The thesis takes as its leitmotif the Prayer of Jesus in John 17 - and the life of Cassidy is discussed alongside reflections of and in relation to Jesus’ prayer for in his Apostles ( and those who follow) in the hours before his passion. The ‘marks’ in Jesus’ prayer have been identified as: Mission, Glory, Unity, Love, Truth, Holiness, Spirituality, Joy, Successive Chapters on each of these appear in the thesis. An analysis of Cassidy’s witness and mission was made through a survey with 120 respondents to measure the effect of Cassidy’s ministry. The chapter on Joy deals with this. The final chapters deal with an assessment of Cassidy’s life and work. The first of these looks at the dynamics of leadership and a critical assessment of his peers and others. The last chapter on “The measure of the man” attempts to list and clarify special significances, abilities and characteristics that have contributed to a unique calling and contribution to our understanding of Lay Apostolicity. / Thesis (PhD)--University of Pretoria, 2010. / Science of Religion and Missiology / unrestricted