By exploring communication and social practices employed during negotiations at the papal court, this volume sheds light on a wide range of sources for studying the high and late medieval papacy. Analyzing the terminology and practice of the "stilus curiae" in documents from all parts of Europe, this volume puts forward a new understanding of negotiation and conflict resolution at the papal court in the Middle Ages. "Stilus curiae" usually refers to the language and style of curial documents, and it is often used to describe the customary application of legal procedure in court practice. The authors of this volume, however, argue for a broader understanding of "stilus curiae" as an umbrella term that encompasses all forms of communication and social practices used during negotiations at the papal court. This volume (the first of two) publishes the results of a research network funded by the German Research Foundation (DFG). Through analysis of the concept(s) of the "stilus curiae", the chapters throw new light on a wide range of sources from the High and Late Middle Ages, including chronicles, biographic and polemic texts, as well as administrative sources, such as letters of petitioners and proctors, speeches, and financial records of ambassadors. Thus, the volume offers a new approach towards the papacy between 1100 and 1500.