Marten Micron (ca. 1500-1559), one of the pastors in the Dutch Church in London, thought about questions concerning visiting and belonging to the church, and wrote his answers in Van de weerdicheydt, nutheydt ende noodicheyt der christelicker vergaderinghen (On the Worthiness, Bene t and Necessity of Christian Assemblies), published posthumously in 1561. In this study Micron's last book is analysed and placed within the context of his life and times. In addition to bringing Micron's answers to the forefront, it also o ers the rst thorough biography of Micron in English and presents a new way of looking at the sharply debated Reformation of the Refugees.