The official language is Mongolian. The number of speakers across all its dialects may be 5.7 million, including the vast majority of the residents of Mongolia. Each group has its Mongolian dialect. During several centuries of intense contact between the groups or, on the contrary, of insulation, lexical peculiarities have emerged locally. Mutual understanding persists in spite of regional particularities. Today, at the end of a long effort, Mongolian language of the northern group includes the language spoken by the southern group. Communication with the dialects “oirat”, profoundly changed by contacts with former Turks, is more difficult. In addition to the 2.5 million people in Mongolia, there are over 2 million speakers of various Mongolian dialects in China, 400 000 speakers of Buryat and around 100 000 speakers of Kalmyk in Russia. The major obstacle to understanding between Mongolian from different countries lies in the gradual abandonment of the dialects of their group to the Russian or Chinese, outside Mongolia.