British missionary Lesslie Newbigin (1909-1998) was a highly influential missionary theologian, a bishop in the Church of South India, and a leader in the twentieth century ecumenical movement. His writings regarding the missionary nature of the church, the engagement of the post-Christendom West as a mission field, and the theological understanding of mission from a Trinitarian perspective have been foundational for both the missional and emerging church movements. This article presents an overview of one aspect of Newbigin’s thought, which, though constituting a key element of his Trinitarian theology of mission, has often been overlooked—his grasp of the role of the Holy Spirit in mission. This author asserts that Newbigin’s pneumatology of mission can help the church, particularly in the West, to understand more clearly how it is to relate to the Holy Spirit as it seeks to participate with God in His mission.