This article introduces a comparative element to the study of the fundamentalist–modernist controversies of the late 1920s, demonstrating that similar ideas are manifested differently in different spatial contexts. Although fundamentalism is primarily considered an American phenomenon, the article argues that the concerns animating fundamentalists in the United States also caused fierce debates elsewhere. It uses three heresy trials – in Belfast, Amsterdam and Stellenbosch – as case studies. In each case, the participants were part of an international Calvinist network, sharing the vast majority of their intellectual commitments and ecclesiastical structure. Yet these shared intellectual commitments did not result in the same outcomes when each group attempted to confront the idea of ‘modernism’ using their church disciplinary procedures. This study demonstrates that social and historical factors played a decisive role in the outcome of each trial. In Belfast, the violent legacy of the recent Irish War of Independence and partition of Ireland lent extra weight to calls for restraint and Protestant unity. In Amsterdam, the social structure of ‘pillarisation’ meant that debates were largely confined within one denomination, and so could be contested more fiercely. In Stellenbosch, meanwhile, the question of how the church should approach the fraught issue of race was the key factor.