A diplomatic style primarily requires clarity and precision. For each topic, each word is selected, corresponding to the specifics of the diplomatic language. The article is devoted to the diplomatic language and diplomatic documents. Their classification and main features are considered. The article discusses the features of the vocabulary of the diplomatic office. It has been proved that the analysis of the lexical system of the language within the framework of thematic lexical groups of the diplomatic department makes the lexical material available for reading in various aspects. It is recommended to classify thematic lexical groups according to the criteria of a diplomatic document. Explanations are given to the concepts of types of diplomatic documents, individual notes, oral notes, partial notes, memorandums, declarations. The diplomatic language has its own vocabulary and lexical and semantic basis. The stylistic features of the diplomatic language were also taken into account, the status of which is the language of interethnic communication. The requirements for the registration of diplomatic documents have been determined.