This volume reprints 25 essays by the author, written between 1962 and 2002, on pontifical diplomacy between the 13th and 17th centuries. The collection of these texts in a single volume sheds light on continuities and developments that are often obscured by the chronological limitations of other publications. The texts are divided into two sections: "the pontifical chancery in the Middle Ages" and "Pontifical diplomacy in the modern era." French text.