The status of certain varieties in the Mongolic group—whether they are languages distinct from Mongolian or just dialects of it—is disputed. There are at least three such varieties: Oirat (including the Kalmyk variety) and Buryat, both of which are spoken in Russia, Mongolia, and China; and Ordos, spoken around Inner Mongolia's Ordos City.

There is no disagreement that the Khalkha dialect of the Mongolian state is Mongolian. Beyond this one point, however, agreement ends. For example, the influential classification of Sanžeev (1953) proposed a "Mongolian language" consisting of just the three dialects Khalkha, Chakhar, and Ordos, with Buryat and Oirat judged to be independent languages. On the other hand, Luvsanvandan (1959) proposed a much broader "Mongolian language" consisting of a Central dialect (Khalkha, Chakhar, Ordos), an Eastern dialect (Kharchin, Khorchin), a Western dialect (Oirat, Kalmyk), and a Northern dialect (consisting of two Buryat varieties). Some Western scholars propose that the relatively well researched Ordos variety is an independent language due to its conservative syllable structure and phoneme inventory. While the placement of a variety like Alasha, which is under the cultural influence of Inner Mongolia but historically tied to Oirat, and of other border varieties like Darkhad would very likely remain problematic in any classification, the central problem remains the question of how to classify Chakhar, Khalkha, and Khorchin in relation to each other and in relation to Buryat and Oirat. The split of [tʃ] into [tʃ] before *i and [ts] before all other reconstructed vowels, which is found in Mongolia but not in Inner Mongolia, is often cited as a fundamental distinction, for example Proto-Mongolic *tʃil, Khalkha /tʃiɮ/, Chakhar /tʃil/ 'year' versus Proto-Mongolic *tʃøhelen, Khalkha /tsooɮəŋ/, Chakhar /tʃooləŋ/ 'few'. On the other hand, the split between the past tense verbal suffixes -sŋ in the Central varieties vs. -dʒɛː in the Eastern varieties is usually seen as a merely stochastic difference.

In Inner Mongolia, official language policy divides the Mongolian language into three dialects: Southern Mongolian, Oirat, and Barghu-Buryat. Southern Mongolian is said to consist of Chakhar, Ordos, Baarin, Khorchin, Kharchin, and Alasha. The authorities have synthesized a literary standard for Mongolian in China whose grammar is said to be based on Southern Mongolian and whose pronunciation is based on the Chakhar dialect as spoken in the Plain Blue Banner. Dialectologically, however, western Southern Mongolian dialects are closer to Khalkha than they are to eastern Southern Mongolian dialects: for example, Chakhar is closer to Khalkha than to Khorchin.