This volume explores how conflicts between secularist ideologies and religious faiths shaped global history in the twentieth century. The chapters approach the dynamic effects of these struggles by focussing on ‘apologetics’, i.e. the discourses, strategies and institutions deployed by religious and secularist actors on the front lines to articulate the faith and defend against the enemy. From the futurology of HG Wells to Cold War evangelicalism to the contentious negotiations over Islam between Communists and the royal house in 1970s Morocco, apologetics is here revealed to be a key site interaction across ideological boundaries. By bringing the dynamics of religious and secular apologetics into a comparative perspective, with examples drawn from Western Europe, the USSR, the USA, North Africa and Asia, the chapters offer new perspectives on the religious dimension of local and global religious politics between the First World War and the end of the Cold War.