Based on the Tibetan loanwords in an archaic Mongolic language, the author reconstructed an unknown Tibetan dialect which pertains to the North Eastern Archaic Tibetan group. The result is compared with the data known from other NEAT dialects, with the material of the West Archaic Tibetan languages such as Balti, Purig and Ladak, and also with the non-archaic dialects from Central Tibet and Lhasa. With the use of Literary Tibetan and data from Old Tibetan, Tibeto-Mongolica proposes a new approach to the reconstruction of the history of the Tibetan language. Originally published in 1966, and long out of print, the book has served as a standard handbook for historical Tibetan studies for several generations of scholars and is now updated by a new Introduction and enhanced by reprints of a selection of the author’s relevant Tibetological papers.