The investigation of Orkhon monuments ha s great importance not only form the historical, political, cultural, but also historical-dialectological point of view. Orkhon monuments are the richest sources for the historical investigation of modern Turkish languages. The study of phonovariants of common language elements existing in the majority of modern Turkish languages on the basis of Orkhon monuments enable the study of more ancient layers of all- Turkish dialectology. For example, a lot of words, like arıg//arı (pure), artuk (extra), azuk (foodstaff), beg\\beg (bay), ber\\ver(give), bitig\\pitik (booklet, writing), ilteber (high, great address, a rank), sub\\suv (water), çabış (military man), beriki (forward), bark (house), tamgacı (stamper), yagı (enemy) found in Orkhon monuments prove their being of the same roots with the modern Turkish languages. The researches, carried out on the languages of Orkhon monuments, show common use of Oguz, Kipchak, Pechenek, Uygur, Selçuk tribal language elements in all Turkish languages and their important role in the formation of Turkish literary language.