What strategy is principally used in diplomatic language? What is the frequency of using vagueness by diplomats and statesmen? What are the basic principles that govern the use of vagueness in diplomatic language? What are the functions that vagueness takes on in diplomatic language? The book focused on these questions and presented a thorough analysis of the phenomenon from the perspectives of Cooperative Principle and the Politeness Principle. It is mainly aimed to extend the Cooperative Principle and the Politeness Principle to cover a special sphere of social communication—language in diplomacy and disclose the nature of vagueness in diplomatic language as well as the language strategy in diplomacy. Practically, it enables readers to gain a better understanding of vagueness in diplomacy, and is helpful for diplomats’ interpretation and analysis of diplomatic language.