The challenge of building relationships of authentic mutuality across lines of difference is an increasingly critical concern in the Christian church and the larger society. Despite decades of work to overcome racism and the legacy of colonialism, cross-cultural relationships are still marred by misunderstanding, an imbalance of resources, and the risks of paternalism and dependence. In the church, these issues often come into focus in mission work, both domestic and international. This research explores the potential and the obstacles to the formation of just relationships through the careful examination of a case—the mission partnership between the Pentecostal Church of Chile and the United Church of Christ. These two denominations, from different branches of the global church but with a shared commitment to ecumenism, undertook multiple shared programmatic activities that facilitated encounters that made possible enduring friendships, despite the obstacles created by differences in language, culture, religious practice, and economic development. The study employs a mixed methodology located within practical theology, including the construction of a history of this partnership through the use of archival materials, a discussion of the history of ecumenical conversation about partnership in the global church, analysis of the similarities and differences between Pentecostal and Reformed Christians, a review of research on short-term mission trips, and an ethnographic presentation of a cross-cultural immersion program for youth from the two churches. It concludes with a discussion of friendship as a theological and sociological term, based in part on semi-structured interviews with partnership participants in both churches. The study finds that despite multiple challenges, this partnership endured because of institutional commitments made by denominational leaders and the willingness of individual members of both churches to participate in partnership activities. In addition, participants demonstrated diverse expressions of friendships with each other, despite the many barriers and impediments to relationship building. The study has implications for other kinds of international partnership and cross-cultural work in both Christian mission and nongovernmental organizations. It reveals some of the characteristics that allow international partner relationships to form and endure. It also identifies the practices of encounter, intentionality, mutual respect, patience, and attentiveness that help to build cultural competencies.