Lyudmyla L. Dmitro Ivanovich Yavornitskiy, as a historian of the Ukrainian Cossacks.

The whole documental heritage of D. Yavornitskiy in the research of the Ukrainian Cossacks is studied for the first time in the dissertation. There are carried out the scientist's methodological foundations and method of researches, his conception of history of the Ukrainian Cossacks and there is figured out the place of the scientist's work in historiography. Yavornitskiy was the first in historiography, who involved into his research of history of the Ukrainian Cossacks a huge amount of the historical sources of different types, kinds, varieties and gave an independent value to an environment as a historical source. The scientist provided an extraordinary contribution into the expansion of the source base of the research of the Zaporozhian Cossacks. His conception was a new word in the explanation of many aspects of history and caused further development of historiography. D.Yavornitskiy's works brought an invaluable contribution not only into the Ukrainian history of the Cossacks' time but also into the history of Ukraine of the XVII - XIX century in general.