The Khalkha or Kalka (Mongolian: Халх, romanized: Halh, Mongolian script:ᠬᠠᠯᠬ᠎ᠠ pronounced [ˈχɑɮχ], Chinese: 喀爾喀) have been the largest subgroup of Mongol people in modern Mongolia since the 15th century. The Khalkha, together with Chahars, Ordos and Tumed, were directly ruled by Borjigin khans until the 20th century; unlike the Oirats, who were ruled by Dzungar nobles or the Khorchins, who were ruled by Qasar's descendants.

The two original major Khalkha groups were ruled by the direct male line descendants of Dayan Khan. The Baarin, Khongirad, Jaruud, Bayaud and the O'zeed (Ujeed) became Dayan Khan's fifth son Achibolod's subjects, thus formed the Southern Five Halhs. Seven northern Khalkha otogs: 1) Jalairs, Olkhonud; 2) Besut, Iljigin; 3) Gorlos, Keregut; 4) Khuree, Khoroo, Tsookhor; 5) Khukhuid, Khatagin; 6) Tanghut, Sartuul; 7) Uriankhai became Dayan Khan's youngest (could be third) son Geresenje's (Mongolian: Гэрсэне Жалайр Хан) subjects. Khotogoids are close in culture and language to the Khalkha Mongols.

There were also numerous direct descendants of Genghis Khan who had formed the ruling class of the Khalkha Mongols prior to the 20th century, but they were and still also regarded as Khalkha Mongols rather than belonging to a special unit.

The Thirteen Khalkhas of the Far North are the major subethnic group of the independent state of Mongolia. They number 1,610,400 (78.8%) of Mongolia's population (1989 figures).

The Khalkha or Halh dialect is the standard written language of Mongolia.