The diplomatic mission of the Holy See is a little-known and often underappreciated facet of the Church's life. Not only does this work provide an invaluable network of intra-ecclesial communication, ensuring the universality and unity of the Church through the maintenance and strengthening of bonds of communion, it also extends to the interaction of the Holy See with other sovereign states. In this article the history and development of the diplomatic work of the Holy See is presented, together with an overview of the principal means by which such work is carried out.