This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book provides a synthesis of previous scholarship on relations between the Mongols and the Catholic world and goes beyond it by offering new approaches and conclusions, sometimes based on author’s own earlier work on the Mongols. It explains the meagre harvest of the mission by reference not just to the distances involved, or to the small number of missionaries, or to linguistic problems, but also to the universe the Mongols themselves inhabited and in particular to their preoccupations in matters of religion, Nature and magic. In the study of contacts between the two distinct cultures which are covered in the book, there has sometimes been a tendency to explain things by entering a verdict of mutual incomprehension. The book argues that the majority of Western observers were lukewarm about an alliance precisely because they recognized Ilkhanid ambitions for what they were.