This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book seeks to explore the variety of ways in which apocalyptic and reformist thought intersected between the late Roman Empire and the twelfth century. It shows that writers of didactic treatises and episcopal legislation collapsed past, present and future, so that apocalyptic thought was an integral part of a ‘call to conversion in the present’. The book examines the intersections through one of Venerable Bede’s lesser-studied works, the poem On the Day of Judgement. It explores ways in which apocalyptic rhetoric was used and shaped by struggles for influence in Italy at the end of the tenth century. The book also examines the ways in which people sought to talk about new crises in the sixth and seventh centuries in order to help prepare for death and, by extension, the Last Judgement.