This book offers a commentary on the Arusha Call to Discipleship, unpacking the meaning of its 12-part summons. It provides an up-to-date theological and missiological view on a major ecumenical mission document with a personal reflection on the state of the world desperately in need of change and transformation. It intends to be a key resource for discovering what it means to become what Pope Francis described as "missionary disciples". Primarily meant for individuals and study groups in churches, mission agencies and theological institutions, it is a useful tool for anyone interested in the ecumenical mission movement and World Christianity. This small book aims to supply a commentary to assist anyone seeking to understand, and respond to "The Arusha Call to Discipleship" (the Call). The Call is a statement on the meaning of Christian mission in today's context that was issued by the Conference on World Mission and Evangelism held by the World Council of Churches (WCC) in Arusha, Tanzania, in March 2018. The conference was the latest in a sequence of conferences, held roughly every ten years, that have attempted, on an ecumenical basis, to take account of the meaning of the mission to which followers of Jesus Christ are called.1 To mention the word "mission" is immediately to step into contested territory. Long gone is the easy complacency that assumed the superior Western world would send missions to benighted and primitive communities in the non-Western world to shape them in its own image. Far from being regarded as heroic pioneers of civilization and progress, the Western missionaries are now more likely to be derided as fanatics who set out to impose their belief system in situations where it was neither needed nor welcome. At the same time, "mission" is a term that has found new currency in contemporary times. Many organizations will proudly display a mission statement that tells you what they are all about.