The present thesis consists of an introduction and the following papers: The aspect-evidentiality system of Middle Mongol. Ural-Altaic Studies, 13. (forthcoming) The tense-aspect system of Khorchin Mongolian. In: Pirkko Suihkonen &amp; Lindsay Whaley (eds.), Typology of Languages of Europe and Northern and Central Asia. Amsterdam: John Benjamins. (forthcoming) Aspect and epistemic notions in the present tense system of Khalkha Mongolian. Acta Linguistica Petropolitana. (forthcoming) Factual vs. evidential? - The past tense forms of spoken Khalkha Mongolian. In: Ad Foolen, Helen de Hoop, &amp; Gijs Mulder (eds.), Empirical Approaches to Evidentiality. Amsterdam: John Benjamins. (under review) Its purpose is to give an account of tense, aspect and evidentiality in three Mongolian varieties: Middle Mongol (MM) as spoken in the Mongol Empire, Khalkha Mongolian as spoken in the Mongolian state, and Khorchin Mongolian as spoken in eastern Inner Mongolia, China. MM started out with a tripartite tense distinction and a medium-sized aspectual system. Its past evidential system was tripartite with suffixes for firsthand, non-firsthand and evidentially neutral information. In Khorchin, which developed under the influence of Mandarin and Manchu, evidentiality was lost, and tense was simplified into a past / non-past distinction, alongside with a discontinuous proximal future / past marker. The aspect system underwent some changes, but retained its complexity. Khalkha, which developed under the influence of Turkic and Tibetan, underwent some shared innovations with Khorchin, but retained participles as a multifunctional unit within finite predicates, so that its aspectual system grew more complex. The past evidentiality distinctions of MM were basically retained, but the introduction of present tense evidentiality brought a number of changes: the evidentially neutral value shifted to signaling assimilated knowledge, and discontinuous future uses were introduced for all past markers. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Accepted. Paper 2: Accepted. Paper 3: Accepted. Paper 4: Submitted.</p><p> </p>