The emergence of so-called “mission congregations” around the turn of the century within the Christelijke Gereformeerde Kerken in the Netherlands (CGKN) confronted this denomination in a very direct way with the question of how to give shape to being a church in a missionary context.This study aims at contributing to finding an answer to that question. It examines the missionary ecclesiological debate as it took place in the global missionary movement of the 20th century. This debate reveals that mission is to be understood as part of the plan of salvation of the Triune God, and that He Himself takes care of its realization. It is His mission, the missio Dei. The church is not only the fruit of this mission of God but is also included and involved in His mission. The church is the community of the Kingdom of God that in the time between the ascension and the return of Christ is engaged in the ongoing execution of the missio Dei.This study, further, examines this theme by focusing on four influential missionary theologians in the reformed context in the Netherlands, Johan Herman Bavinck, Hendrik Kraemer, Johannes Verkuyl and James Lesslie Newbigin. Next to these theological voices, the missiological discussion as it developed within the CGKN is studied. What is contributed by this discussion, both by formal and normative “voices” and by workers in the “mission congregations”? In bringing together all these voices, in its conclusions, this study shows fundamentals and necessary elements needed in looking for an ecclesial structure to be a witnessing church today. The church participates in God’s mission.Jan van ’t Spijker (1960) is a pastor in the Christian Reformed Churches. From 1997 to June 2005, he served as a missionary in Mozambique. From 2008 he is lecturer of missiology and evangelism at the Theological University Apeldoorn. In addition to missionary subjects, he is also teaching in the area of pastorate and diaconate. He is an adviser of the Deputies for Foreign Mission, and of the Deputies for Evangelism.